000 - DSCV-SA FAQ - Front Cover Rev 02 - SPX · PDF fileAre specialist field service engineers or ... (ITP) SPX reserves the ... Piping design engineers often use the turbine bypass

FREQUENTLY ASKED

QUESTIONS

DSCV‐SA FREQUENTLY ASKED QUESTIONS

DSCV‐SA FAQ:140109 ‐01 WHERE SMART SOLUTIONS MEET GLOBAL POWER GENERATION

DSCV‐SA FAQs – INDEX MECHANICAL DESIGN 1. What are the materials of construction?

a. Pressure boundary, castings & forgings. b. Trim c. Water branch thermal sleeve

2. What are the connection types and sizes available? 3. Are noise attenuating trims available? 4. What is the bonnet design, bolted or pressure seal and is it high temperature extended? 5. Is the trim balanced?

a. Benefits of high pressure balancing versus low pressure balancing. b. HP Balancing vs LP Balancing Table

6. Does the plug have anti‐rotation? 7. Is an inlet steam strainer available? ACTUATION 8. What actuation is available and stroking speeds?

a. Pneumatic i. Single & double acting

b. Hydraulic i. Hydraulic Power Units (HPU) and PLC control. ii. Self‐contained actuators

c. Electric 9. Instrumentation OPERATION 10. What is the minimum water pressure required? 11. Does the DSCV‐SA have tight shut off? 12. Does the DSCV‐SA have an outlet diffuser? 13. What is the rangeability, turndown, of the DSCV‐SA? 14. Is there a minimum outlet steam velocity required to prevent cooling water drop out?

a. Advantages of steam atomisation versus spray nozzles 15. Are dump tubes available? INSTALLATION 16. Distances;

a. What is the minimum upstream straight line length? b. What is the minimum downstream straight line length? c. What is the minimum distance to the temperature sensor? d. What is the minimum distance to the pressure sensor? e. What is the minimum distance to the dump tube?

17. Can the DSCV‐SA be installed horizontally and is there anything to consider when installing horizontally? 18. Are thermal liners required? 19. Does the valve require warming and draining? 20. Material & pipe class transitions? 21. Where should the water control valve be positioned? 22. Are hydro and steam blowing trims available? 23. Are control algorithms available for bypass to condenser? MAINTENANCE 24. Are any special tools required? 25. Are specialist field service engineers or special training required? 26. Does the valve have ‘Quick‐Change’ trim design? MANUFACTURE 27. Typical inspection and test plan (ITP)

SPX reserves the right to incorporate our latest design and material changes without notice or obligation. Design features, materials of

construction and dimensional data, as described in this bulletin, are provided for your information only and should not be relied upon

unless confirmed in writing.

Page 1 of 2

DSCV-SA FAQs – 1a: MECHANICAL DESIGN: Pressure Boundary

Piping design engineers often use the turbine bypass valve or steam letdown valve as the point to transition pipe class both for

pressure rating and material grade.

The DSCV-SA is an angle style valve. Normally the DSCV-SA is ordered and supplied in a split pressure rated design. The inlet part of the

body will be of a higher pressure class than the outlet. The same is true for the for the pressure boundary materials with the inlet

often being supplied in a different grade of material to the outlet.

Body – Inlet: The body inlet is the high pressure & temperature side. The standard body is produced from a casting in low alloy steels

ASTM A217 WC6, WC9 and C12A or carbon steel ASTM A216 WCB. Forged bodies and other material grades can be supplied on

request.

If forged bodies are preferred the body is supplied in the following standard materials

The bonnet will be supplied in the same material grade as the body, either cast or forged.

Standard Cast Body Inlet Materials (high pressure side)

ASTM A216 WCB

ASTM A217 WC6

ASTM A217 WC9

ASTM A217 C12A

Standard Forged Body Inlet Materials (high pressure side)

ASTM A105

ASTM A182 F11

ASTM A182 F22

ASTM A182 F91

ASTM A182 F92




Page 2 of 2

Body – outlet: The body outlet is the lower pressure side. The standard body outlet is produced from a forgings in low alloy steels

ASTM 217 WC6, WC9 and C12A or carbon steel ASTM A216 WCB.

Forged Body Outlet Materials (Low pressure side)

ASTM A105

ASTM A182 F11

ASTM A182 F22

ASTM A182 F91

The outlet diffuser which produces the customer outlet

connection can be made of a different material than the

DSCV-SA outlet section so as to meet the customer pipe

material and prevent on-site dissimilar welds.




Page 1 of 1

DSCV-SA FAQs – 1b: MECHANICAL DESIGN: Valve Trim

The trim is designed to expand equally with the pressure boundary in which it is contained to prevent high thermally induced stresses.

A mandatory requirement of severe duty valves is that the plug is fully guided for stability. Therefore all guiding surfaces are hardened

to a value of greater than 50 on the Rockwell C scale. This prevents any mechanical galling between the guiding surfaces.

The Seat is similarly hardened to > 50 Rockwell C. Although uncommon on bypass valves and not required a Stellite deposit on the seat

can be supplied if specifically requested by the customer. Stellite is a more soft material, approximately 35 on the Rockwell C scale and

thus more prone to wear. However as Stellite® is softer it can be machined if the seat becomes damaged. Normally a Stellite® seat is

only specified by a very specific request due to a customer preference.

Stem Options:

17-4 PH Stainless steel

316 Cond ‘B’

A182-F91

A565 (616) Type 422

Upper Guide & Anti Rotation

68-72 Rockwell C

Heavy Duty Distribution Spacer: A217 WC9

Pilot Plug: 410 Stainless steel

68-72 Rockwell C

Main Plug: A182 F22 or A217 WC9

52-56 Rockwell C

Cage A182 F22 or A217 WC9

52-56 Rockwell C

Atomising nozzle: 410 Stainless steel

68-72 Rockwell C




Page 1 of 1

DSCV-SA FAQs – 1c: MECHANICAL DESIGN: Cooling Water Branch Thermal Sleeve

When the temperature differential between the maximum inlet steam temperature and the minimum cooling water temperature

exceeds 2200C (400

0F) then a thermal sleeve is fitted. The thermal sleeve is a 316L stainless steel tube which the cooling water passes

to the steam atomising head. This sleeve produces an annular gap between its outside diameter and the inside diameter of the water

branch. This gap or thermal barrier protects the water branch from high thermally induced stresses.

The sleeve is seal welded at one end which allows it to freely expand and contract within the water branch.




Page 1 of 2

DSCV-SA FAQs – 2: MECHANICAL DESIGN: Connection Types & Sizes

The DSCV-SA was designed with maximum flexibility in mind with regards to connections. When employed in a power station the vast

majority of DSCV-SA installations have butt weld end connections. On small biomass plants, petrochemical, pulp & paper or similar

industries where the DSCV-SA is used as a steam let-down station, the connections are generally flanged.

The DSCV-SA has both options weld ends or flanged ends.

Body – Steam Inlet Connection: Normally the body is produced from a casting. The body casting has two formats, weld end or flanged.

When the customer steam inlet connections cannot be achieved then an expander can be welded to the body inlet connection and, if

required, a flange also. Therefore any steam inlet connection in terms of size, type or material can be accommodated.

Butt weld end.

Note the drilled disc is only

for the factory hydro

pressure test

Standard casting with

steam inlet expander

Flanged end.

The flange is an integral part of the

casting.




Page 2 of 2

Body – Steam outlet connection: The DSCV-SA outlet section is fully formed from a forging. Therefore full flexibility is available to

produce any size, connection type or material.

Butt Weld, with or

without material

transition.




Page 1 of 1

DSCV-SA FAQs – 3: MECHANICAL DESIGN: Noise Attenuating Trim Options

The DSCV-SA has several noise attenuating trim options. As standard the DSCV-SA is fitted with the Copes-Vulcan single stage HUSH™.

The valve can also be fitted with either a multi stage HUSH™ trim or the multi disc, multi labyrinth RAVEN™ trim.

All of the trim options have active noise control throughout the full valve stroke and flow range. 1, 2 and 3 stage HUSH™ trims are

available in standard trim configurations. Multi stage RAVEN™ trims are available upon request. The final pressure drop occurs through

the final outlet diffuser, see FAQ sheet 11.

IMPORTANT: The noise levels shown on the Copes-Vulcan data sheets are calculated to the internationally recognised Aerodynamic

noise prediction method; IEC 60534-8-3:2000. Other manufacturers show noise prediction levels based on their own in-house

calculation routines, however these have not been internationally qualified or accepted.

Note: A number of bypass valve suppliers employ inlet and trim exit baffles for noise attenuation. However these are passive noise

control elements as they have a fixed CV and only truly attenuate at one flow rate, normally maximum flow rate. As the flow rate

reduces the passive baffle has little or no influence on the pressure drop and thus little or no noise attenuation.

Single stage HUSH II

or HUSH III™

RAVEN™

Multi disc,

multi path

labyrinth

Multi stage HUSH™,

2 & 3 stage trim options are

available as standard options.




Page 1 of 1

DSCV-SA FAQs – 4: MECHANICAL DESIGN: Bonnet Designs

The DSCV-SA has two bonnet types, bolted and pressure seal.

Pressure classes: ANSI 150 through and including ANSI 900: Bolted Bonnet.

Pressure classes: ANSI 1500 and higher: Pressure Seal Bonnet.

Cooling extended bonnets are supplied on most DSCV-SA. If the inlet steam temperature is above 2500C (482

0F) then extended cooling

bonnets are fitted as standard.

The cooling extension is designed to protrude 200mm (8 inches) to 300mm (12 inches) out of standard insulation thicknesses,

depending on the size of the DSCV-SA.

The standard gland packing set is a lower carbon guide bushing, preformed Graphoil rings and a 431 stainless steel gland follower.

Spring, live loaded packing is available with all bonnet options.

Bolted Bonnet

Pressure Seal Bonnet.




Page 1 of 3

Turbine bypass valves are quite large and unbalanced trims on the majority of applications are not used due to the enormous

actuation and stem forces that would be generated. Therefore the vast majority of trims in turbine bypass valves are balanced. The

easiest and most economical method of balancing the trim is ‘low pressure balancing’. Most other designs employ low pressure or P2

balancing; however, these low pressure balancing systems rely on auxiliary balancing seals such as piston rings and close tolerance

sealing surfaces to prevent the high pressure steam unbalancing the trim. In operation, if these seals or surfaces wear or become

damaged, the trim quickly becomes unbalanced and stem loads dramatically increase and fluctuate which can result in the valve

oscillating violently or even unable to open on command.

The shutoff class and tight shutoff is also totally dependent on the performance of the balancing component parts. Tight shut, FCI 70-2

Class V, can be demonstrated in the factory with a newly assembled valve when piston rings and close tolerance sealing surfaces of the

balancing cylinder are new. However, due to minimal wear or damage/scratching by small metallic particles in the steam on a new

build power station the tight shut off will be lost.

Copes-Vulcan, during the early stages of the design of the DSCV-SA made the conscious decision to move away from low pressure

balancing and hence remove all the risks and problems associated with low pressure balancing, witnessed numerous times on power

stations.

HIGH PRESSURE BALANCING or P1 balancing is a key design feature of the DSCV-SA for reliable smooth operation. This design feature

cannot be emphasised enough.

Benefits of high pressure balancing;

� HIGH PRESSURE BALANCING works in harmony with the dynamics of the high pressure steam rather than being in

constant ‘battle’ with the high pressure steam trying resist it flowing into the low pressure areas of the trim.

� NO piston rings, sigma seals, etc. that wear and without very regular maintenance, cause:

o Dramatically increases seat leakage.

o Induce trim instability, dramatically increasing stem and actuator thrusts as the trim starts to go out of balance.

o Bypass valve not opening to command signal as the leakage rate past the piston rings becomes so large the out of

balance forces of the plug are too great for the actuator.

� NO close tolerance balancing cylinder surfaces that wear and become scratched with entrained small metallic debris in the

steam. Without very regular maintenance, cause:

o Dramatically increases seat leakage.

o Induce trim instability, dramatically increasing stem and actuator thrusts as the trim starts to go out of balance.

o Bypass valve not opening to command signal as the leakage rate past the piston rings becomes so large the out of

balance forces of the plug are too great for the actuator.

� NO piston rings or seals required to be purchased as commission spares or held in the power plant stores as maintenance

inventory or insurance spares.

These benefits are very significant to the power plant owner and operator as high pressure balancing not only reduces

maintenance and inventory costs but also removes the risk of the valve becoming unstable which may force an unscheduled

maintenance outage. With repeatable tight shut off the DSCV-SA is also thermodynamically efficient by not leaking expensive high

pressure steam.

The benefits for the EPC designing and erecting the power plant are reduced commissioning spares, a design that is more

tolerant to entrained debris in the steam and thus giving far more confidence during commissioning and reliability runs.

DSCV-SA FAQs – 5: MECHANICAL DESIGN: Trim Balancing




Page 2 of 3

One of the key components of the high pressure balancing system is the E-A ring which has three important functions;

• Ensuring uniform high pressure steam pressure has unrestricted flow porting to both the top and bottom of the valve plug.

• Provides upper plug guiding for plug stability.

• Has an integrated and substantial plug anti-rotation key.

E-A Ring E-A Ring forms an integral part of the heavy duty

distribution spacer

Anti-Rotation Key

3 equally spaced

plug guides

4 high pressure

steam flow ports Main plug with pilot plug

removed for clarity




Page 3 of 3

The DSCV-SA valve has a very tight shut off in the

closed position, as a minimum ANSI FCI 70-2 Class V.

It achieves this tight shut off by utilising a pilot plug

design so that in the closed position the main plug is

unbalanced with the full steam pressure acting on

the top of the plug, white arrows indicating the

steam pressure force on the plug. This load

combined with the actuator thrust resulting in very

high seat contact loads, which ensure a very tight

shut off.

Not only is tight shut off required for plant thermal

efficiency it also prevents leak induced ‘wire drawing’

damage across the seat which would otherwise

result in frequent maintenance to repair or replace

the seat.

When the DSCV-SA first opens the pilot plug opens

and high pressure inlet steam floods the underside of

the main plug. The plug is now high pressure

balanced, high pressure steam is now on the bottom

of the plug as well as the top.

With the steam atomising nozzle connected to the

main cage the steam atomising unit is now operating

in preparation to receive the incoming cooling water

from the water control valve.

The pilot plug CV is several times larger than the

atomising nozzle which ensuring high pressure

balancing.

As can be seen high pressure steam is freely allowed

to flow both to the top and bottom of the plug,

ensuring high pressure balancing.

The balancing system has NO piston rings or close

tolerance balancing cylinders that can become worn

or damaged.

Risk of piston ring wear or breakage is negated √High risk of valve instability and failure due to piston ring

wear X

Risk of balancing cylinder wear or damage is negated √High risk of valve instability and failure due to balancing

cylinder wear or damage. X

Risk of balancing cylinder & plug wear or damage is

negated √High risk of valve instability and failure due to balancing

cylinder & plug wear or damage. X

Designed for maximum forces that can be applied. √Only designed for low pressure forces and risk of stem

breakage if balancing is lost. X

Designed for maximum forces that can be applied. √Only designed for low pressure forces and risk of

insufficient actuator thrust available if balancing is lost. X

No maintenance, No inventory. √ Require regular maintenance and high inventory costs. X

With low pressure balancing a sealing arrangement is required to prevent the

high pressure fluid from entering the low pressure side, normally the top side,

of the plug. When the fluid is steam then due to the temperatures this seal is a

piston ring. Piston rings wear in service and as they wear then the leakage rate

increases. This increase in leakage rate continues to increase until the pilot

plug cannot evacuate the high pressure steam from the low pressure side of

the plug at a an equivalent rate. Therefore the pressure on the upper side of

the plug increases which actuation forces. These increased actuator forces

induce instability in the actuator and trim and eventually lead to the valve not

opening on command or event stem breakage.

LP Balancing requires balancing components

High Pressure versus Low Pressure Trim Balancing Comparison Table

Maintenance

Actuator Size

Stem Breakage

BALANCING CYLINDER

& CLOSE TOLERANCE

PLUG

BALANCING CYLINDER

PISTON RINGS

High Pressure Trim BalancingBALANCING

COMPONENTS

HP Balancing does not require balancing components LP Balancing requires balancing components

With high pressure balancing NO balancing components are required. In fact

rather than having specific sealing components to continuously battle high

pressure steam from entering the low pressure balancing areas, with high

pressure balancing the high pressure steam is encouraged to enter all areas.



of the plug. The balancing cylinder is required for the piston rings to operate

in. The inside surfaces of the balancing cylinder must have finely machined

surfaces for the piston rings to seal. These surfaces are susceptible to wear

and damage. Any small particle debris in the steam that enters the balancing

cylinder will score the surfaces and induce leakage and stem wire drawing.

This will cause loss of balancing, instability, possible failure of the valve to open

on command and stem breakage.

Low Pressure Trim Balancing

HP Balancing does not require balancing components












of the plug. The balancing cylinder is required for the piston rings to operate

in. The inside surfaces of the balancing cylinder must have finely machined

surfaces for the close tolerance plug to seal. These surfaces are susceptible to

wear and damage. Any small particle debris in the steam that enters the

balancing cylinder will score the surfaces and induce leakage and stem wire

drawing. This will cause loss of balancing, instability, possible failure of the

valve to open on command and stem breakage. With a close tolerance plug

and balancing cylinder any small debris will induce mechanical galling and

possibility of the plug jamming in position.

HP Balancing by design ensures correct stem diameter and strength.LP Balancing by design dictates the stem diameter and strength are

not sufficient is low pressure balancing is lost.

By design the stem size, diameter, and strength is suitable for full HP forces

that can be applied.

The stem size, diameter, and strength are only designed for the low pressure

balancing forces. Therefore if the balancing is lost then the stem will be

subjected to forces far beyond those it is designed for. This leads to stem

breakage.

HP Balancing dictates the actuator is sized for the maximum forces

that can be applied.

LP Balancing by design dictates the actuator is only sized for the low

pressure balancing forces.

By design the actuator is sized for the maximum forces that can be applied by

the high pressure steam.

The actuator in low pressure balanced valve designs is only sized for the low

pressure balanced thrusts generated. Therefore if partial or all of balancing is

lost then the actuator will have insufficient thrust available, become unstable

and may not even have sufficient thrust to open the valve.

As there are no balancing components then there is no maintenance or spare

parts that are required to be held in the plant's inventory.


Low pressure balancing components, piston rings, balancing cylinder, close

tolerance plug are all maintainable items. As wear accumulates, especially if

the valve is mounted horizontally, all these parts will require maintenance.

Piston rings, balancing cylinders and close tolerance plugs will all have to be

held in the plant stores. These parts are critical to the valve performance and

therefore classified as critical spares (insurance spares) and not just

recommended spares.




Page 1 of 1

DSCV-SA FAQs – 6: MECHANICAL DESIGN: Plug Anti-Rotation

With large trims and especially large plugs rotational forces generated in the trim can be substantial. The magnitude of the

rotational forces generated in a specific application and often unique installations is almost impossible to calculate or model.

Therefore the DSCV-SA has an integrated anti-rotation key in the inlet heavy duty distribution spacer and matching key way in the

plug. Therefore the risk of plug rotation and the damage that can cause is eliminated. The whole design philosophy of the DSCV-SA

is, if any potential risk can be eliminated, it is.

E-A Ring

E-A Ring forms an integral part of the heavy duty

distribution spacer

Anti-Rotation Key

3 equally spaced

plug guides

4 high pressure

steam flow ports Main plug with pilot plug

removed for clarity




Page 1 of 1

DSCV-SA FAQs – 7: MECHANICAL DESIGN: Integral Steam Strainer

Although the DSCV-SA is quite tolerant to entrained debris in the steam as it has no piston rings, close tolerance balancing systems

and natural self-clearing through the integral steam atomising nozzle it can be fitted with an integral steam inlet strainer. The

strainer has a 3.0mm (0.118 inch) screen as per the requirements of TRD 421. The stainless steel screen is fixed to the outer

diameter of the heavy duty inlet steam distribution spacer. The steam inlet strainer is an optional extra and should be requested

at time of enquiry. It can also be supplied as an upgrade to installed DSCV-SA.

Heavy duty inlet distribution spacer fitted

with 3.0mm screen steam strainer

Standard heavy duty inlet

distribution spacer




Page 1 of 2

DSCV-SA FAQs – 8a: Actuation: Pneumatic

There are two types of pneumatic actuation within the Copes-Vulcan range, CV-700 & CV-1000 series spring opposed diaphragm

actuators and CV-P800 single and double acting piston actuators. Pneumatic actuation represents approximately 80% to 85% of all

the turbine bypass systems supplied, the rest being hydraulically actuated. The benefits of pneumatic actuation are significantly

lower capital costs, reduced maintenance and no fire risk. Hydraulic actuation when using mineral oil can initiate a fire if an oil

leak drips onto a hot surface.

Typical stroking speeds for turbine bypass systems are;

• Normal modulation; 10-15 seconds.

• Emergency fast mode (turbine trip): less than 1 to 3 seconds.

Actuation thrusts; as standard and unless specified differently by the customer all actuation thrusts calculated for the DSCV-SA are

increased by a 30% safety factor.

Hand wheels; all models of pneumatic actuator have a hand wheel option. Generally side mounted with an additional top

mounted option for the CV-700 series.

Only the smaller size DSCV-SA with relatively low thrust requirements short strokes will be fitted with the CV-700 or CV-1000

series diaphragm actuators. The majority of DSCV-SAs will be fitted with the CV-P800 piston actuators.

The CV-P800 piston actuator is either single acting with opposed spring or double acting. Due to the thrust requirements and

stroke lengths most DSCV-SAs will be fitted with the CV-P800 double acting piston actuator.

CV-700 Series Diaphragm Actuator

Spring Opposed

Hand wheel top or side mounted

Low thrust

Limited to a maximum of 125mm stroke (5 inches)

CV-1000 Series Diaphragm Actuator

Spring Opposed

Hand wheel side mounted

Low to medium thrust

Limited to a maximum of 75mm stroke (3 inches)




Page 2 of 2

The CV-P800 double acting piston actuator is by far the most common actuator fitted to the DSCV-SA. Occasionally where thrusts and

stroke lengths allow single acting units with springs are fitted.

When an ‘air fail’ safety position is required, ‘Air Fail Closed’ or ‘Air Fail Open’, then an air volume tank will be supplied. Depending on

the volume of air required the volume tank will either be mounted directly on the actuator or supplied as a vertical free standing tank.

All air volume tanks are supplied as standard to ASME VIII div.1 design.

CV-P800 Series Piston Actuator

Single or double acting

Hand wheel side mounted

High thrust

Limited to a maximum of 300mm stroke (12

inches), longer on request.

Typical Hook-Up drawing for double acting CV-P800 piston actuator, modulation stroking speed <10 seconds,

air fail open with emergency fast open trip <2 seconds.




Page 1 of 5

DSCV-SA FAQs – 8b: Actuation: Hydraulic

HYDRAULIC ACTUATORS WITH COMMON HYDRAULIC POWER UNIT (HPU)

Hydraulic actuation was the norm for turbine bypass valves. However over the last 15 years or so pneumatic actuation is now very

much the predominant choice for power stations up to 600MW. Pneumatic actuation is far less costly, significantly lower on-site

maintenance and has no fire risk associated with it unlike the mineral oil used on hydraulic systems. However some power

engineering contractors and/or their customers still prefer hydraulic systems. In the power industry the actuators are motivated

by hydraulic oil supplied from a common HPU (Hydraulic Power Unit). These HPUs can supply just a single bypass system or

multiple bypass systems. Generally each system is design to suit the specific requirements of that power plant.

Below is a typical example of a single HP bypass system with a single HPU supplying the hydraulic oil to the HP bypass valve, water

control valve and water block valve. The hydraulic valves and control panel are mounted on the HPU.




Page 2 of 5

Below is a typical example of a HP, HRH & LP bypass systems with a single HPU supplying the hydraulic oil to all the bypass valves,

water control valves and water block valves. With these systems the oil accumulators are normally located on the local hydraulic

valve panels, close to the valves. This eliminates the need of large bore hydraulic pipe between the HPU and hydraulic valve

panels.

The actuators are relatively standard double acting pistons. The cylinder will contain a micro-pulse transducer for position feedback.

On most applications the actuators are also fitted with end of travel limit switches. Drip trays are normally also fitted on the HP bypass

actuator to prevent any hydraulic mineral oil dropping onto a hot surface. The two hydraulic connections on the actuator should be

connected to the hydraulic oil supply stainless pipe work via high pressure flexible hoses. This prevents any strain on these

connections. The actuators are perfectly suitable for installation either vertically or horizontally.

Copes-Vulcan does not manufacture the actuators or the HPUs. These are supplied via a number of specialist hydraulic companies that

Copes-Vulcan has worked with over many years.




Page 3 of 5

The HPUs have a number of standard features although each one will be contract specific to meet the exact requirements of

the project and site.

• Skid mounted with drip tray or full capacity bund (oil spill capture).

• Motor Pump Set: Dual pump sets are provided with automatic change over capable of charging the accumulator storage

station in a time suitable for the application. Nominal power for each pump would be 2kw to 4 kw, depending on HPU

size with an electrical supply of 400/480 volt AC 3 phase 50 or 60 Hz. Other voltages upon request.

• Accumulator Storage: The HPU will normally be supplied with sufficient storage for 3 operations of each valve, ie

close/open/close. With certain installations the accumulator storage can be mounted local to the valve along with the

hydraulic control valve panel.

• Filtration: An independent motorised filtration unit is fitted to the HPU requiring a power supply of 0.37 kw and can also

be used for filling or draining the reservoir. Being an independent unit also allows for changing the filter element without

switching off the HPU.

• Oil Cooling: An air blast cooler will be fitted within the system installed within the filtration unit and requiring a power

supply of 0.37 kw. If preferred a small heat exchanger can be fitted using the power plant’s utility water.

• System Condition Monitoring: Hydraulic system pressure, level and temperature can be visually monitored on the HPU.

In addition the following monitoring instrumentation is available.

o Pressure transducer for;

� Pump Stop/Start and Auto Change Over

� System High Pressure

� System Low Pressure

� System Low/Low Pressure

o Oil Level Switch; Indicates and alarms Low Level and Low/Low Level

o Oil Temperature; Indicates and alarms high oil temperature

o Filter Condition; Indicates and alarms when filter is blocked and in bypass mode

o Pump running signal; indicates which pump is running, operational or standby

• Hydraulic Control System: Mounted either on the HPU or local to the valves, within an IP65 enclosure, and comprises of a

logic manifold assembly to include for the following functions;

o Proportional Control for positional accuracy and fast response

o Solenoid Control for Fast Open and/or Fast Close

o Speed Control and Pressure Control

o Utilisation for all required fail safe positions

NB: A key feature of our design is that all hydraulic solenoid valves, including the positioning solenoid valves, within our

system are zero leakage. This ensures that when the bypass valves and water valves are in a static position there is no

requirement for the motorised pumps to make up system pressure to compensate for leakage within normal spool type

solenoid valves. This reduces power requirements and eliminates the need for continuous oil cooling.

• Electronic Control: The system will be controlled using a PLC having inputs and outputs both digital and analogue. Local

display of the signals, system status and settings is provided using a 100mm (4”) HMI operator display mounted on the

electronic panel door. The PLC is as standard will be a Siemens S7 series. Typical I/O interface with the power plant’s DCS

is shown below.




Page 4 of 5

Below is a typical Input/Output exchange between the HPU and the power plants DCS.

Typical HPU

Electrical Control Panel

Hydraulic Control Panel

Accumulator

Pumps & Motors

Air Blast Cooler

Oil Reservoir

HMI Touch

Screen




Page 5 of 5

TYPICAL HPU (Hydraulic Power Unit)

C O M P A N Y




Page 1 of 1

DSCV-SA FAQs – 9: Actuation: Pneumatic Instrumentation

Copes-Vulcan does not manufacture instrumentation. Therefore Copes-Vulcan is free to offer any manufacturer’s

instrumentation. If no preference is stated by the customer then the positioner of choice will be the Siemens PS2 as SPX Copes-

Vulcan has a global price agreement with Siemens.

Positioners:

• Siemens PS2 (Default)

• ABB TZID-C

• Emerson DVC models

Air Filter Regulators:

• SMC Range (Default)

• Norgren

• Bellofram

Limit Switches:

• Honeywell 1LS-4C (Default)

• Allan Bradley

• NAMCO

Solenoid Valves:

• ASCO (Default)

• MAC

• Skinner

Boosters:

• RK Instrumentation (Default)

• SMC

Quick Exhaust Valves:

• SMC (Default)

Instrument Air Tubing & Fittings:

• 316 Stainless Steel - Parker (Default)

• 316 Stainless Steel - Swagelok

The above is just a sample of the standard default options we would normally choose unless the customer specifications

states differently. We can potentially fit any make and model of instrumentation.




Page 1 of 1

DSCV-SA FAQs – 10: OPERATION

What is the minimum water pressure required?

The DSCV-SA utilises a steam atomising desuperheater with a full venturi section to achieve the desired steam

temperature reduction. As such, the coolant is not Injected into the steam flow as with spring loaded spray nozzle

designs, the coolant is aspirated into the steam flow by utilising a small proportion of the HP Steam flow as the

motive energy source. The coolant pressure required at the DSCV-SA cooling water branch connection therefore

need only be the same pressure as the steam outlet pressure conditions; a small pressure drop should be

incorporated to allow the separate cooling water control valve to ‘control’ the flow of coolant to the DSCV-SA in

response to the system command signal.

With a spring loaded spray nozzle design the “atomisation” of the coolant is achieved by the pressure differential

between the coolant pressure and the outlet steam pressure. This pressure drop causes the coolant to break up

into a wide range of different coolant particle sizes – a large differential pressure will produce smaller coolant

particle sizes, where as a small pressure differential will produce much larger coolant particle sizes. With these

designs of desuperheater it is a fundamental requirement that the pressure differential is maintained as high as

possible in order to achieve a reasonable level of atomisation and subsequently smallest particle size.

Spring loaded spray nozzles are limited in their turndown as the coolant atomisation and spray pattern degraded

as the coolant flow rate and available pressure differential reduces. As the coolant demand reduces, the coolant

control valve closes and the coolant valve trim absorbs the coolant pressure differential leaving little pressure

differential for the spray nozzles. This lack of pressure differential at the spray nozzles does not allow them to

atomise the coolant, leading to the coolant pouring into the steam rather than a fine atomised mist. Mechanical

spray nozzles also rely on the surrounding steam velocity to provide adequate mixing. When the steam load

reduces so does the steam velocity and the ability of mechanical spray nozzles equally reduce. This effect

manifests itself with poor downstream steam temperature control and coolant ‘drop-out’. Coolant drop-out can

be very damaging as cold water will track along the bottom of the inside wall of the downstream pipe whilst un-

cooled superheated steam travels along the top and sides. This produces high thermal shocks which can lead to

steam header fracture.

With the steam atomiser incorporated into the DSCV-SA a pressure differential is NOT required as the atomising

steam flow provides the motive energy required to atomise the coolant. As the atomising steam is at a higher

temperature than the incoming coolant supply the latent heat transfer immediately commences providing pre-

heat to the coolant. This results in a ‘hot fog’ being produced at the atomiser outlet which provides very fine

coolant particle sizes, which are at or close to their temperature of evaporation. This results in the coolant being

quickly absorbed into the main steam flow achieving the desired temperature control in the shortest distance and

negates the requirement for any downstream thermal liners.

This lower pressure coolant supply requirement can also provide operational cost benefits to plant designers and

operators as a much lower pressure (and subsequently lower cost) coolant source can be utilised to maximum

effect without impacting the system performance. The steam atomising flow within the DSCV-SA design pre-heats

the coolant prior to exit of the atomiser and as such is much more accommodating of the lower coolant

temperatures usually associated with lower pressure coolant supplies without the need for thermal liners to be

incorporated at the valve outlet.




Page 1 of 1


What is the minimum water pressure required?

The DSCV-SA utilises a steam atomising desuperheater with a full venturi section to achieve the desired steam

temperature reduction. As such, the coolant is not Injected into the steam flow as with spring loaded spray nozzle

designs, the coolant is aspirated into the steam flow by utilising a small proportion of the HP Steam flow as the

motive energy source. The coolant pressure required at the DSCV-SA cooling water branch connection therefore

need only be the same pressure as the steam outlet pressure conditions; a small pressure drop should be

incorporated to allow the separate cooling water control valve to ‘control’ the flow of coolant to the DSCV-SA in

response to the system command signal.

With a spring loaded spray nozzle design the “atomisation” of the coolant is achieved by the pressure differential

between the coolant pressure and the outlet steam pressure. This pressure drop causes the coolant to break up

into a wide range of different coolant particle sizes – a large differential pressure will produce smaller coolant

particle sizes, where as a small pressure differential will produce much larger coolant particle sizes. With these

designs of desuperheater it is a fundamental requirement that the pressure differential is maintained as high as

possible in order to achieve a reasonable level of atomisation and subsequently smallest particle size.

Spring loaded spray nozzles are limited in their turndown as the coolant atomisation and spray pattern degraded

as the coolant flow rate and available pressure differential reduces. As the coolant demand reduces, the coolant

control valve closes and the coolant valve trim absorbs the coolant pressure differential leaving little pressure

differential for the spray nozzles. This lack of pressure differential at the spray nozzles does not allow them to

atomise the coolant, leading to the coolant pouring into the steam rather than a fine atomised mist. Mechanical

spray nozzles also rely on the surrounding steam velocity to provide adequate mixing. When the steam load

reduces so does the steam velocity and the ability of mechanical spray nozzles equally reduce. This effect

manifests itself with poor downstream steam temperature control and coolant ‘drop-out’. Coolant drop-out can

be very damaging as cold water will track along the bottom of the inside wall of the downstream pipe whilst un-

cooled superheated steam travels along the top and sides. This produces high thermal shocks which can lead to

steam header fracture.

With the steam atomiser incorporated into the DSCV-SA a pressure differential is NOT required as the atomising

steam flow provides the motive energy required to atomise the coolant. As the atomising steam is at a higher

temperature than the incoming coolant supply the latent heat transfer immediately commences providing pre-

heat to the coolant. This results in a ‘hot fog’ being produced at the atomiser outlet which provides very fine

coolant particle sizes, which are at or close to their temperature of evaporation. This results in the coolant being

quickly absorbed into the main steam flow achieving the desired temperature control in the shortest distance and

negates the requirement for any downstream thermal liners.

This lower pressure coolant supply requirement can also provide operational cost benefits to plant designers and

operators as a much lower pressure (and subsequently lower cost) coolant source can be utilised to maximum

effect without impacting the system performance. The steam atomising flow within the DSCV-SA design pre-heats

the coolant prior to exit of the atomiser and as such is much more accommodating of the lower coolant

temperatures usually associated with lower pressure coolant supplies without the need for thermal liners to be

incorporated at the valve outlet.




Page 1 of 4


Does the DSCV-SA have tight shut off?

YES!

The DSCV-SA, unlike many alternative designs, utilises a high pressure balanced plug which is purposefully

designed to work in harmony with the high pressure steam, rather than in a continuous battle to prevent high

pressure inlet steam from leaking to the top side of a low pressure balanced plug design as used in many other

steam conditioning valve designs. The DSCV-SA works with the high pressure steam, and as this is always the

dominant pressure, the DSCV-SA simply cannot become “out of balance”.

The DSCV-SA valve has a very tight shut off

in the closed position, as a minimum ANSI

FCI 70-2 Class V. It achieves this tight shut

off by utilising a pilot plug design so that in

the closed position the main plug is

unbalanced with the full steam pressure

acting on the top of the plug, this load

combined with the actuator thrust

resulting in very high seat contact loads,

which ensures a very tight and repeatable

shut off.

Not only is tight shut off required for plant

thermal efficiency it also prevents leak

induced ‘wire drawing’ damage across the

seat which would otherwise result in

frequent maintenance to repair or replace

the seat.

As can be seen high pressure P1 steam is

directed to the top of the plug and

therefore negates any need for very close

tolerance sealing surfaces or piston rings as

used in low pressure balanced plug designs

that are susceptible to wear and damage.




Page 2 of 4

In the Closed Position both the main plug and pilot plug are

closed.

P1 Pressure is present on top of the plug.

P2 Pressure is present on the downstream of the Plug

When an open command signal is received,

the actuator retracts and the pilot plug is the

first to open. This allows P1 steam to flood

through the large pilot plug port to the

underside of the main plug. The main plug is

now balanced reducing the actuation thrusts

required.

The capacity of the pilot plug port is several

times greater than that of the atomising

nozzle and designed leak paths in the cage

guiding system ensure equal inlet pressure on

the underside and top side of the main plug.

Now with the pilot plug open, high pressure

inlet steam has flooded the underside of the

main plug and the steam atomising unit is

now operating in preparation to receive the

incoming cooling water from the water

control valve




Page 3 of 4

When the Pilot Plug is fully open and engaged with the

Tandem Cap, the main plug begins to open.

Steam Flows through the trim spacer and into the large

feed ports of the plug flow then passes through the cage

where it is pressure reduced prior to exiting the valve via

the integral outlet diffuser plate.

The Principle and Effect of High Pressure Balancing

High pressure balancing can only occur when P1 pressure is present above and below the plug in normal

operation. Flow OVER the web plug designs that utilise piston rings or close tolerance labyrinth seals are low

pressure balanced design with the sealing mechanism trying to prevent the high pressure steam from entering

the low pressure balancing area. This is a constant battle between the high pressure steam and the sealing

mechanism and as a result any wear, erosion or debris damage that is caused to the seal under normal power

plant operating condition can only result in the low pressure balance being lost and causing plug instability or the

plug being unable to open or close on command. In either scenario a low pressure balanced plug causes a plant

risk and must therefore be subject to a rigorous maintenance regime in order to maintain balance. The DSCV-SA

uses a high pressure balancing system which works with the dominant pressure and eliminates all the associated

operational problems caused by low pressure balancing.

In addition to these major operational benefits, a high pressure balanced plug also provides pressure induced seat

contact loading when the valve is closed. This pressure induced seat contact loading occurs when the Main Plug

and Pilot Plug are closed and Full P1 Pressure builds on the top of valve plug. In the closed condition, the DSCV-SA

plug is essentially unbalanced (with high pressure on top of the plug and low pressure beneath the plug) and the

steam pressure acting on this unbalanced plug area provides additional high levels of seat contact load. This

ensures exceptional, continual and repeatable seat tightness.




Page 4 of 4

Pressure Induced Contact Load

The DSCV-SA is designed to exceed the seat leakage requirements as defined in ANSI/FCI 70-2 Class V and is

provided with an actuator suitably designed to provide the correct amount of seat contact load required to

achieve this tight shut off.

In addition to this shut off class being achieved, the DSCV-SA can also meet the requirements of MSS-SP-61 which

requires that an additional seat contact load of 1000 lbf per linear inch of seat diameter be provided. The DSCV-

SA achieves this by utilising pressure induced contact load. Depending on the size of DSCV-SA utilised the

following operational pressures are required to exceed the requirements of MSS-SP-61

DSCV-SA Unit Size

0 1 2 3 4 5 6

MSS-SP-61 Seat Contact

Load lbf 15,284 20,587 26,672 32,563 39,436 48,861 61,428

Minimum operating

pressure to meet the

requirements of MSS-SP-

61 Seat Contact Load

Bar.a

PSIA

59.19

858

43.68

633

33.47

485

27.64

401

22.88

332

18.42

267

14.45

209




Page 1 of 1


Does the DSCV-SA have an outlet diffuser? YES! The DSCV-SA incorporates an outlet diffuser plate into the design that provides many additional features

• Outlet is fully forged piece with diffuser plate integral

• Generates a thermal barrier so no thermal liners are required.

• NO cooling water passes through the diffuser. Therefor no quenching or thermal shock of the diffuser.

• Provides centralised location and robust anchor point for Steam

Atomiser Housing • Provides the Butt Weld End or Flanged Outlet connection which

is matched to the customers required downstream pipe size / pipe schedule requirements

• Provides an outlet material transition if required • Provides BWE Prep for outlet fabrication • Includes test ring for shop Hydrostatic Test

Outlet diffuser plates are designed to operate in conjunction with

the valve trim over the valve’s performance envelope and are

designed per application.

The diffuser plate is available with a multitude of hole sizes for noise consideration and can be provided with high

CV Porting & Flow Guides for low pressure drop applications.

The outlet Diffuser Straightens flow at outlet of the valve and

provides ideal mixing zone for the exit of the steam atomising

desuperheater. The final desuperheating takes place directly after the

outlet diffuser section. With the outlet diffuser aligning the main

steam flow to create an excellent mixing zone the final stage of

desuperheating occurs rapidly and evenly without danger of thermal

shock or water drop out in the downstream pipe work.

Finely atomised and preheated cooling water.

The main steam now at outlet pressure forms a

360 degree annulus that surrounds the finely

atomised preheated cooling water providing a

thermal barrier between the cooling water and

downstream pipe work whilst the cooling water

fully evaporates.




Page 1 of 2


What is the rangeability / turndown of the DSCV-SA?

The DSCV-SA was specifically design to achieve extremely high rangeability/turndown and wide performance

envelopes. This is achieved by the method of cooling water introduction employed, steam atomisation. Steam

atomisation has several benefits over mechanically spraying the cooling water into the steam line.

To achieve high turndowns the unit has to be designed so that it is not dependant on the steam line velocity to

promote mixing and evaporation without cooling water ‘drop-out’. Steam atomisation achieves this as follows;

Pre-Heating: With steam atomisation of the cooling water a significant benefit is the pre-heating of the cooling

water. The atomising steam raises the approach temperature of the cooling water close it its evaporation point.

This promotes rapid final evaporation very quickly after leaving the atomising head. With this preheating no

thermal liners are required to protect the valve or downstream pipe work from thermal shock.

The atomising steam entering the atomising head is accelerated to sonic velocity through a critically designed

converging nozzle. These nozzles are specifically designed for each contract based on the P1 steam conditions to

fully utilise the amount of energy (enthalpy conversion) available. The cooling water is introduced into the steam

atomising head via a converging tube again designed to suit the cooling water rate required to evenly introduce

the steam circumferentially. The venturi effect of the motivating atomising steam exiting the steam nozzle and

the converging/diverging venturi section finely atomise the cooling water and ensure a highly homogenous mix

exiting the steam atomising head. This homogenous mix now enters the main steam which is exiting the diffuser

plate in a ‘hot fog’ or gaseous consistency. Therefore there are no cooling water droplets to fall out.

Note that steam atomisation cooling water introduction should not be confused with mechanical spray nozzles

which present the cooling water into the steam as a spray of liquid and with mechanical spray type

desuperheating, at low steam line velocities water ‘drop out’ can occur.

Therefore there is NO lower limit for steam line velocities for

the Copes-Vulcan DSCV-SA steam conditioning valve. The DSCV-

SA has no dependency on steam line velocity to achieve its

required turndown.

Diagram showing the steam atomising head of

the Copes-Vulcan steam conditioning valve DSCV-SA.




Page 2 of 2

Trim Turndown: The trim is high pressure balanced using a pilot plug. When the DSCV-SA first opens the pilot

plug open and feeds steam to the inner cage area. Attached to the cage is the steam atomising nozzle Therefore

when the pilot plug opens the only forward flow of steam is through the steam atomising nozzle. These nozzles

are contract specific and designed to pass the correct amount of steam for the application, steam pressure and

temperature.

On the diagram shown here only the pilot plug is

open. High pressure steam is allowed to pass

through to the steam atomising nozzle. Water can

be introduced as the atomising steam will pre-heat,

atomise and evaporate the cooling water.

On this diagram the main plug is now open. High

pressure steam now passes through the main cage

and the steam atomising nozzle.




Page 1 of 6


Is there a minimum outlet steam velocity required to prevent cooling

water drop out?

When using a DSCV-SA valve design - NO!

The DSCV-SA was specifically design to achieve extremely high turndowns and wide performance envelopes. With

a DSCV-SA there is NO downstream minimum steam velocity requirement. This is due to the unique method of

coolant introduction utilising a steam atomising desuperheater which incorporates a FULL venturi section. Steam

atomisation has several benefits over mechanically spraying the cooling water into the steam line. To achieve high

turndowns the unit has to be designed so that it is not dependant on the steam line velocity to promote mixing

and evaporation without cooling water ‘drop-out’. Steam atomisation achieves this as follows:

Pre-Heating: With steam atomization of the cooling water a significant benefit is the pre-heating of the cooling

water. The atomising steam raises the approach temperature of the cooling water close it its evaporation point.

This promotes rapid final evaporation very quickly after leaving the atomising head. With this preheating no

thermal liners are required to protect the valve or downstream pipe work from thermal shock.

The atomising steam entering the atomising

head is accelerated to sonic velocity through

a critically designed converging nozzle.

These nozzles are specifically designed for

each contract based on the P1 steam

conditions to fully utilise the amount of

energy (enthalpy conversion) available. The

cooling water is introduced into the steam

atomising head via a converging tube again

designed to suit the cooling water rate

required to evenly introduce the steam

circumferentially. The venturi effect of the

motivating atomising steam exiting the

steam nozzle and the converging/diverging

venturi section finely atomise the cooling

water and ensure a highly homogenous mix

exiting the steam atomising head. This

homogenous mix now enters the main

steam which is exiting the diffuser plate in a

‘hot fog’ or gaseous consistency. Therefore

there are no cooling water droplets to fall

out.

Note that steam atomisation cooling water introduction should not be confused with mechanical spray nozzles

which present the cooling water into the steam as a spray of liquid and with mechanical spray type

desuperheating, at low steam line velocities water ‘drop out’ can occur.

Therefore there is NO lower limit for steam line velocities for the Copes-Vulcan DSCV-SA steam conditioning

valve. The DSCV-SA has no dependency on steam line velocity to achieve its required turndown.




Page 2 of 6

FAQs – 14a: OPERATION

What are the advantages of steam atomisation versus spray nozzles?

The DSCV-SA has a full venturi steam atomising system. This provides excellent water atomisation; preheating and

homogenous mixing resulting is very rapid cooling water evaporation and negates any danger of thermal stress.

In many alternative steam conditioning valve designs a number of mechanical spray nozzles are utilised around

the periphery of the valve’s outlet section. Spray nozzles can only utilise the small amount of energy to atomise

the cooling water that is available from the pressure differential between the steam and cooling water. The

amount of pressure drop across the nozzle reduces as the water flow rate reduces from maximum as more and

more pressure drop is taken across the water control valve to reduce the cooling water flow. The spray pattern

and atomisation produced under minimum flow conditions are even less effective.

The very high thermal transient over the pressure boundary wall where the multiple cooling water nozzle

housings are welded also gives rise to thermal stress induced cracking.

Below is shown a typical example of such a design utilising spring loaded nozzles:

Cooling water is introduced via mechanical

spray nozzles with very high temperature

differentials that can lead to thermal stress

induced failure of the pressure boundary.

The Bypass steam temperature can be

extremely high + 560°C (+1040°F)

The Bypass Cooling Water Temperature can

be quite low, less than 100°C (212°F)

These Applications have an

Enormous Temperature Differential




Page 3 of 6

14a: Operation – Spray Nozzles versus Steam Atomisation

Feature Spring Loaded Spray Nozzles Steam Atomisation utilising

a full venturi section

Injects Coolant into highly

turbulent zone

Provided the spray nozzle is

positioned correctly the

steam turbulence created

by the pressure drop over the valve’s

trim can be utilised to mix the steam

and coolant flow. However, as this

turbulence needs to be carefully

predicted there is a chance this could

result in injected coolant being

‘thrown’ against the downstream

valve or pipe wall, causing thermal

shock.

Injects coolant after pressure

reduction has been achieved

Spray nozzles are usually

positioned after the valve

trim (in the low pressure

zone) at the valve outlet. No coolant is

injected as the steam is pressure

reduced through the valve trim

The steam atomising

desuperheater design is

positioned after the valve

trim and in the low pressure zone at

the valve outlet. No coolant is injected

as the steam is pressure reduced

through the valve trim

Variable Geometry Nozzles causes

atomising efficiency to be

compromised at low coolant flow

rates

A variable geometry nozzle

uses a spring to “vary” the

nozzle discharge aperture

in an attempt to improve atomisation

at low coolant flow rates. This results

in a lower differential pressure

(between steam and coolant) to be

used which increases coolant particle

size and as such the efficiency and rate

of evaporation.

The steam atomising

desuperheater does not

rely on spray nozzles to

perform the atomisation. Atomising

steam flow rate remains constant

(when the valve is open) regardless of

coolant flow rates required and as

such atomising efficiency remains

excellent throughout the range of

operation.




Page 4 of 6



Coolant is injected at the periphery

of the outlet

The coolant is introduced

on the periphery of the

outlet which can cause

issues with thermal shock due to

direct coolant impingement with the

valve outlet and downstream

pipework and in many instances a

thermal liner will be required to

mitigate (but not eliminate) such

thermal shock. On large diameter

outlets the steam flow may suffer

from poor coolant / steam mixing and

temperature stratification further

compounding temperature induced

stress.

The DSCV-SA Atomiser

outlet is purposefully

positioned at the CENTRE

of the valve outlet. The intimately

mixed fluid exits the venture section

with the consistency of a ‘hot fog. As

the cooling water is finely atomised

and pre-heated the final

desuperheating takes place directly

after the outlet diffuser section. With

the outlet diffuser aligning the main

steam flow to create an excellent

mixing zone the final stage of

desuperheating occurs rapidly and

evenly without danger of thermal

shock or water drop out in the

downstream pipe work. As final

evaporation occurs very quickly then

the required downstream straight line

lengths are kept to an absolute

minimum.

Nozzles can be removed from the

body housing and maintained

The spring loaded nozzles

contain a number of

moving parts that are

subject to differential thermal cycling

and fluid induced erosion. Access to

these for maintenance purposes is

provided for this reason

The DSCV-SA Steam

atomiser contains no

moving parts. The steam

atomising nozzle is attached to the

valve cage that can be removed via

the valve bonnet. The combining tube

and venturi section are considered

maintenance free items, but can be

removed from the valve should this be

required.

Requires a thermal liner when ΔT

between coolant / steam exceeds

250°C

With spring loaded nozzle

designs of desuperheaters

that are placed around the

periphery of the valve outlet the

potential for thermal shock can be

high. To mitigate (but not eliminate)

this problem thermal liners are often

required due to the temperature

differential between steam and

coolant. These are permanent fixtures

that are incorporated into the valve

outlet which cannot easily be

inspected or replaced should the

thermal liner fail.

Due to the unique method

of coolant introduction via

the steam atomising

desuperheater with a full venturi the

coolant is preheated close to its

evaporation temperature prior to

exiting the atomiser venturi section

into the downstream pipework. As the

temperature differential between

steam and water is not substantially

reduced and that this ‘hot fog’ is

introduced at the centre of the valve

outlet NO Thermal liners are required.




Page 5 of 6



Venturi used for homogenous

mixing & preheat of coolant

With a spring loaded

nozzle, no “pre-heat” is

applied and the coolant is

injected at temperature. There is no

homogeneous mixing as the

desuperheating principle relies upon:

Sufficient pressure drop to be taken

over the nozzle to atomise the coolant

– this pressure drop reduces at low

coolant flow rates with an exponential

increase in mean coolant particle size.

The mixing of the steam and coolant is

totally reliant upon the downstream

velocity to suspend the coolant

particles in the flow whilst preheating

and evaporation takes place.

Subsequent temperature stratification

is totally reliant upon downstream

turbulence provide by the steam

velocity

Desuperheaters of this design will

require a MINIMUM of 5 – 6 meters

per second (1000 to 1200

feet/minute) steam velocity to avoid

coolant drop out.

The DSCV-SA is the only

steam conditioning valve

available today that utilises

a venturi within the desuperheater

design to provide maximum

preheating and mixing of the coolant

prior to entering the main steam flow.

This results in a ‘hot fog’ being created

at the atomiser outlet which results in:

a. Rapid evaporation

b. Eliminates the risk of thermal

shock by preheating the coolant to

close to its evaporative

temperature

c. Minimal straight pipe lengths

being required downstream.

Expanded HP Steam used to

minimise coolant particle size

Spring loaded spray nozzles

rely totally on the pressure

differential between the

coolant supply and steam pressure to

atomise the coolant into particles.

When coolant flow rates are reduced,

this results in a smaller pressure

differential being available (as the

coolant pressure reduces the nozzle

area closes under the induced spring

load to reduce flow rate) This smaller

pressure differential results in larger

coolant particle sizes at low coolant

flow rates.

The DSCV-SA utilises an

innovative design to use a

small proportion of the HP

Steam within the steam atomising

desuperheater. This HP Steam is

integrally and automatically supplied

to the desuperheater when the trim

first begins to open. The HP Steam is

expanded through a critical nozzle at

which point coolant is introduced to

the steam. This expanded HP Steam

produces an instantaneous release of

energy which is transferred to the

incoming water flow. The

homogeneous mixture of expanded

HP Steam and coolant is then forced

through a converging venturi section

to further preheat and mix the flow

and accelerate it to produce a very

fine coolant particle size that produces

a ‘hot fog’ at the desuperheater

outlet.




Page 6 of 6



Simple method of HP Steam

Extraction and coolant

introduction & maintenance

Coolant is introduced via a

number of nozzles located

around the periphery of

the valve outlet. The number of

nozzles used determines the

maximum coolant flow rate that can

be achieved. These spring loaded

nozzles contain a number of moving

parts that are subject to differential

thermal cycling and fluid induced

erosion, thus increasing valve

maintenance time and the number of

components required to be replaced.

HP Steam extraction is not utilised in

the spring loaded spray nozzle design.

Within the DSCV-SA all HP

Steam extraction used

within the steam atomising

desuperheater is performed internally

to the valve and automatically with no

external control required. Coolant is

regulated via a separate coolant

control valve.

The steam atomising nozzle is

attached to the valve cage that is

removed via the valve bonnet. The

combining tube and venturi section

are considered maintenance free

items, but can be removed from the

valve should this be required.

The DSCV-SA requires minimal

maintenance due to its many design

features and should maintenance be

required this can be achieved

expediently without the need for

special tooling or service personnel.




Page 1 of 8

DSCV-SA FAQs – 15 OPERATION

Are Dump Tubes Available?

YES!

Dump tubes are used in conjunction with the DSCV-SA valve in bypass to condenser applications and provide a

back pressure at the valve outlet. This limits the intermediate discharge pipe specific volume and therefore

velocity resulting in a smaller valve outlet connection and subsequent discharge piping.

The use of Dump Tubes on a Turbine Bypass to Condenser application also provide the following benefits:

• Reduce Valve & Discharge Pipe Size (Lower Installed Cost)

• Ensure thorough mixing of coolant / steam prior to entry into condenser which protects the tube bundles

from high temperature ‘pockets’ or water erosion

• Reduces system ‘Bypass’ system noise

• Used as ‘flow meters’ as part of a feed forward control system

All dump tubes are custom engineered to the specific application and are designed to complement the

requirements of the bypass valve, condenser and plant noise level requirements

Single Stage Dump Tubes • Designed for ONE stage of pressure drop

• Consists of a number of holes drilled around the periphery of the tube with axial discharge

• Typically provides between 1.5 – 3.0 bar (20 - 45 PSI) back pressure to bypass valve at full flow (Noise

level dependant)

• Simple Construction, lowest cost

• Multiple Hole Size for ‘best’ noise fit

• Constructed from ASTM A335 P11 (EN 10216-2 13CrMo4-5 (WERKSTOFF 1.7335) as standard

• Multiple mounting options

• Flanged

• Butt Weld

• Mounting Cap




Page 2 of 8

Single Stage Dump Tube with butt weld inlet connection

Single Stage Dump Tube With Flanged Inlet Connection

Single Stage Dump Tube with Butt Weld Inlet

Connection and material Transition

Two Stage Dump Tubes • Designed with Two stages of pressure drop

• Stage 1 – Inlet Diffuser Plate

• Stage 2 – Drilled holes in periphery of tube with axial discharge

• Typically provides between 2.0 – 5.0 bar (30 – 75 PSI) back pressure to bypass valve at full flow (Noise

level dependant)

• Stages are designed for optimal pressure drop and noise characteristics



• Flanged

• Butt Weld

• Mounting Cap




Page 3 of 8

Two Stage Dump Tube with Mounting Cap

Two Stage Dump tube with

mounting cap installed in the

condenser ductwork.

Three Stage Dump Tubes • Designed with Three stages of pressure drop

• Stage 1 – Inlet Diffuser Plate

• Stage 2 – Internal Cone with Drilled Holes

• Stage 3 – Drilled holes in periphery of tube with axial discharge


level dependant)

• Stages are designed for optimal pressure drop and noise characteristics



• Flanged

• Butt Weld

• Mounting Cap




Page 4 of 8

1st

Stage

1500 off ¾” (19mm) holes

CV = 27500

2nd

Stage (not Shown)

4000 off ½” (12mm) holes

3rd

Stage

11616 off 5/16” ( 8mm) holes

CV = 30000

12 equi-spaced arrays




Page 5 of 8

End Discharge Dump Tubes

• Designed with single stage of pressure drop

• Specifically designed to meet installation constraints

• Generally used on Water Cooled Condensers to avoid tube bundle impingement.


level dependant)

• Designed for optimal pressure drop and noise characteristics



• Flanged

• Butt Weld

• Mounting Cap

End Discharge Dump Tube with

Flanged Inlet Connection




Page 6 of 8

Installation Depending on the ‘type” of condenser being used will ultimately determine the design and placement of the

dump tube in relation to the condenser. We shall discuss the installation arrangement for both water cooled

condensers and air cooled condensers.

Water Cooled Condensers

On a Water Cooled Condenser

the dump tube connection can

be on the inlet to the condenser.

Flow Discharge holes of the

dump tube should be positioned

away from the tube bundles

On water cooled condensers it is

common to arrange the dump tube

discharge holes in two 90° Arrays.

The Dump Tube discharge is directed

away from turbine exhaust and the

tubes of the condenser

The Dump Tube is positioned at the

inlet neck to the condenser and not in

the interconnecting ducting between

the turbine exhaust and condenser

inlet.

In designing the dump tube it is important to know the type of condenser that will be utilised as this will dictate

the discharge hole pattern arrangement.




Page 7 of 8

Air Cooled Condensers

Direct Insertion into the Condenser Duct

Direct insertion of the dump tube into the condenser duct work is an acceptable installation provided the

following parameters are met:

• The ‘Shadow’ created by the dump tube insertion should be less than 5% of the total Duct Area. Shadows’

higher than this percentage may affect turbine back pressure and MW output and may not be acceptable

to the turbine manufacturer.

• SPX should be advised to ensure discharge hole pattern is developed accordingly

• Dump Tube Discharge holes are positioned facing directly downstream

Multiple Dump tubes in the array can be accepted providing that

the maximum 5% shadow parameters can be achieved and that a

minimum distance between each insertion is maintained to

ensure flow discharge distribution is not adversely affected.




Page 8 of 8

Air Cooled Condensers

Indirect Insertion into the Condenser Duct

When, due to the physical requirements of the dump tube for the application, a direct insertion cannot meet the

maximum ‘shadow’ criteria an alternative indirect insertion can be made. This requires a suitably dimensioned

branch connection on the duct work to allow for installation of the dump tube.

In this indirect insertion method, the dump tube discharge holes are positioned through 360 degrees, thus

resulting in a shorter overall length. The branch connection withdraws the majority of the discharge area from the

turbine exhaust flow and as such the minimum ‘shadow’ criteria can be met. The diameter of the branch is

carefully calculated to ensure that velocities remain within acceptable limits and do not cause a source of

secondary noise generation.




Page 1 of 5

DSCV-SA FAQs – 16a: INSTALLATION

What is the minimum upstream straight line length?

The DSCV-SA has been specially designed to meet market requirements for compact installation. The Heavy

Duty distribution spacer negates the requirement for any straight length at the inlet of the DSCV-SA. Long

Radius Bends or Isolation Valves can be fitted directly at the valve inlet.




Page 2 of 5

FAQs – 16b: INSTALLATION

What is the minimum downstream straight line length?

Straight lengths are required after the valve to allow the evaporative process to take place.

Exact distances are calculated based on the thermodynamic parameters of the application and are shown on the

DSCV-SA valve data sheets.

Factors Effecting Downstream Straight Length Requirements

• Residual Superheat in outlet flow

• Coolant Supply Temperature

• Inlet Steam Pressure & Temperature (This determines the available ‘energy’ through the atomiser)

• Valve Application (is a dump tube fitted?)

And ultimately

• Downstream Velocity

The Parameters above are used to determine an evaporative time. This is multiplied by the maximum steam

velocity to determine a minimum straight length distance

As a general ‘rule of thumb’ an evaporative time of between

0.05 and 0.1 seconds is achieved with the DSCV-SA Steam Atomiser.

Multiply this evaporative time by velocity to determine the required distance




Page 3 of 5

FAQs – 16c: INSTALLATION

What is the minimum distance to the temperature sensor?

Straight lengths are required after the valve to allow the evaporative process to take place.

Exact distances are calculated based on the thermodynamic parameters of the application and are shown on the

DSCV-SA valve data sheets.

The downstream temperature sensor length after the DSCV-SA, is needed for the water to totally complete its

vaporization into steam before interfacing with the temperature sensor in a feedback control system.

If the water has not completely vaporized, the resulting input control data will be inaccurate due to moisture

contacting the sensing temperature element. The exact length required after the valve is a function of several of

the factors previously described.

The temperature sensor can be located after a downstream bend (if fitted) and this may prove beneficial to the

quality of the final temperature reading. Any entrained water that still exists after the minimum straight line

distance from the DSCV-SA has been reached will be forced out of the flow by centrifugal forces as the flow

passes around any downstream bend.

As a general ‘rule of thumb’ a factor of 0.18 - 0.2 seconds

multiplied by the maximum pipe velocity should be applied,

with a minimum recommended distance of 10 meters.




Page 4 of 5

FAQs – 16d: INSTALLATION

What is the minimum distance to the pressure sensor?

Pressure Recovery at the valve outlet will be almost instantaneous and a minimum distance of 1.5m (5ft) should

be allowed before placement of the pressure sensor.

Specific requirements from the sensor manufacturer should be sought to highlight any ‘special’ requirements of

the sensor type / manufacturer. As with any feedback device incorrect placement of the sensor (too close or too

far away) could result in faulty measurements or a slow system response time




Page 5 of 5

FAQs – 16e: INSTALLATION

What is the minimum distance to the dump tube?

Dump tubes are used in conjunction with the DSCV-SA valve in bypass to condenser applications and provide a

back pressure at the valve outlet. This limits the intermediate discharge pipe specific volume and therefore

velocity resulting in a smaller valve outlet connection and subsequent discharge piping.

When a dump tube to condenser is employed we are targeting an enthalpy value or temperature at the discharge

of the dump tube (into the condenser duct) and as such the intermediate temperature between the DSCV-SA

valve outlet and the dump tube inlet will not reach a dry saturated steam equilibrium as excess water (called

dryness fraction) is usually carried along with the saturated steam flow to ensure the dump tube discharge

conditions are met.

Exact distances are calculated based on the thermodynamic parameters of the application; however the following

‘rule of thumb’ can be applied

Where Coolant / Inlet Steam flow rates are less than 15%

• A distance of 0.05 seconds x maximum velocity should be applied with a minimum distance of 3 meters

(10 feet) (straight length) being maintained.

Where Coolant / Inlet Steam flow rates are greater than 30%

• A distance of 0.1 seconds x maximum velocity should be applied with a minimum distance of 5 meters (17

feet) (straight length) being maintained.




Page 1 of 1

DSCV-SA FAQs – 17: INSTALLATION

Can the DSCV-SA be installed horizontally and is there anything to

consider when installing horizontally?

The DSCV-SA can be installed in ANY

orientation although ‘common sense’ would

dictate not to install the valve with the

outlet vertically upwards to assist with ease

of maintenance.

Actuators and yoke assemblies are designed to be

‘self-supporting’ and require no additional supports

regardless of the intended orientation of

installation

For installation other than vertical (Actuator vertical, outlet vertically downwards) consideration should be given

to the requirement for service assistance fixtures as covered in FAQ section 24.




Page 1 of 1


Are Thermal Liners Required? Definition: Thermal liners are used to protect the steam pipe from sudden thermal shocks in the event cooling

water is directly sprayed onto them through poor desuperheater design and/or coolant drop out.

Examples of Thermal Shock Caused by Poor desuperheater design and coolant impingement

• The use of a thermal liner is dependent upon the type of desuperheater design used within the bypass

valve and the prevailing temperature (steam / coolant) conditions

• The thermal liner is used to prevent secondary thermal stress issues caused by the atomisation method

• The thermal liner should be fixed at one end and free at the other to allow independent thermal

expansion / contraction

The DSCV-SA DOES NOT REQUIRE A THERMAL LINER TO BE USED (see FAQ 12)




Page 1 of 9


Does the Valve Require Warming and Draining?

Drains are generally required both upstream and downstream of any steam conditioning valve

• Drains are required to protect the valve and piping system by collecting and removing free ‘water’

that may have accumulated within the system

• This free ‘water’ may be as a result of condensation when the plant is shut down or the system

inactive or can be as a result of a cooling water control system malfunction or incorrect setting

• Free ‘Water’ located upstream of the valve has the potential to be very damaging to valve trim

components

• Free ‘Water’ located downstream of the valve present problems for piping, other instrumentation

and can affect the temperature control efficiency

Experience with many installed bypass valve systems indicates that water collection in the piping is probably the

most frequent single root cause for operating problems.

If water / condensate accumulates in the bypass piping and is not drained properly during plant start-up, this can

cause system damage and a loss potential. Typical problems associated with water accumulation are water

hammer, erosion or loss of temperature control through accumulated water.

Water hammer can lead to excessive damage in the plant with long downtimes and consequent lost production.

Erosion problems in the piping can lead to expensive replacement or repair and causes excessive losses due to

leakage and heat rate degradation over long operating periods.

Condensate can form and collect in the bypass piping during plant start-up, when the pipe walls are being heated

by the steam flowing through the pipes. Condensate can also form during normal operation when there is no flow

through the bypass valve system and the pipes are kept warm by condensation, this can be eliminated by allowing

the Bypass valves and inlet piping to remain at or close to the normal operational temperature.

Under start-up conditions, condensation is unavoidable and the condensate must be removed through the piping

system drains. If pipe layout drawings of the bypass system are provided, SPX can review the piping and drain

arrangement prior to installation. A pipe with 1% slope back to the main steam pipe will be self-draining when the

bypass valve is not in operation. However when the bypass is in operation and steam is flowing to the bypass

valve, condensate will not flow back to the main steam pipe.

The piping configuration and orientation of installation will determine if the system is self-draining or if an

additional valve body drain needs to be provided. This valve body drain is positioned at the lowest point on the

high-pressure side of the valve. Automatic drain valves or manually actuated drain valves can be used (not

supplied by Copes-Vulcan), however the operation of these drains during plant start-up and warming must be

incorporated into the site procedures to ensure that the piping system and body of the DSCV-SA valve are free

from condensate prior to operation of the valve. Irreparable damage can be caused to the valve trim components

IF high velocity condensate is forced through the valve trim.




Page 2 of 9

Inlet Drain Locations depending on valve orientation

Vertical Installation (Horizontal Inlet, Outlet Downwards)

In this orientation an upstream drain

should be positioned at the lowest

point of the inlet piping. The inlet

pipe should slope away from the

valve inlet to ensure sufficient

drainage is achieved when the valve

is not in operation.

Horizontal Installation (Vertical Inlet, Outlet Horizontal)


should be positioned at the lowest

point of the inlet piping. The inlet

pipe should slope away from the

valve inlet to ensure sufficient

drainage is achieved when the valve

is not in operation.

Drain

Drain




Page 3 of 9

Drain

Drain

Horizontal Installation (Vertical Inlet, Outlet Horizontal)

In this orientation it is recommended

that the valve body be provided with

an integral body drain connection

point (drain system by others). This is

because the inlet of the valve body is

the lowest point in the piping system

and will cause natural drainage into

the valve inlet. Care must be taken to

ensure any condensate formed and

collected in the valve body in this

orientation can be suitably removed

prior to operation of the valve.

Vertical Installation (Horizontal Inlet, Outlet Vertically Upwards)


should be positioned at the lowest point

of the inlet piping. The inlet pipe should

slope away from the valve inlet to

ensure sufficient drainage is achieved

when the valve is not in operation.

This orientation of installation is NOT RECOMMENDED

due to difficulties caused in suitable drain provision and

difficulties in executing maintenance operations




Page 4 of 9

Drain

Outlet Drain Locations

The drain should be positioned at the LOWEST point in the piping after the valve. It is recommended NOT to make

the valve the lowest point to avoid accumulation issues. The slope to outlet drain should never be less than 100:1




Page 5 of 9

VALVE WARMING

Preheating of the Steam Conditioning valve is not always necessary and depends on the nature of the application

and the intended installation.

Preheating of the Steam Conditioning valve ensures metal temperatures are kept elevated and reduces:

• Condensate formation within the valve and piping system

• Thermal shock of the valve body and trim components (on high temperature applications)

There are many types of preheating system that can be utilised and the selection is generally based upon

• Creating a system that provides sufficient preheat and drainage

• Minimizing the system energy loss when utilising preheating steam

• Is the installation indoors or outdoors

• The Temperature difference at the outside of the insulation and the ambient temperature

• The Distance between the valve and the live steam line




Page 6 of 9

Preheating System examples

Generally in this installation

additional preheating would not

be required providing that the

distance between the valve inlet

connection and steam header is

kept to a short distance.

Note that in this orientation an

integral valve body drain would

also be recommended.

Preheating System – Natural Circulation

Main Steam Line

Drain

Cir

cula

tio

n L

ine

Bypass valve with a natural

circulation system. The

circulation pipe must be

insulated to maintain thermal

efficiency.

The DSCV-SA valve is provided

with a preheating connection

stub on the high pressure inlet

side of the valve for connection

to the circulation line at site (by

others)




Page 7 of 9

Preheating System – Balanced Pressure Drop

This method is the most energy efficient installation as little system heat loss is experience. This system does

require a suitable design to ensure anticipated pressure drop between the preheating line take off and the

subsequent inlet connection return.

With a suitable system design it should be possible to have a sufficiently large flow of steam through the system

to keep the valve body and inlet piping at a suitable temperature and subsequently free of water.

The DSCV-SA valve is provided with a preheating connection stub on the high pressure inlet side of the valve for

connection to the circulation line at site (by others)

Main Steam Line

Drain

Pre

he

ati

ng

Lin

e




Page 8 of 9

Preheating System – Utilising a Higher Pressure Steam Source

This method can be energy efficient however it can substantially increase the amount of piping required to

complete the preheating line. Again, the DSCV-SA valve is provided with a preheating connection stub on the high

pressure inlet side of the valve for connection to the circulation line at site (by others)

Main HP Steam Line

Pre

he

ati

ng

Lin

e

Hot Reheat (HRH) Steam Line




Page 9 of 9

Preheating System – Upstream and Downstream Preheating

This method is the most common and usually easiest way of preheating the upstream piping leg. A preheating

flow passes from the high pressure inlet to the lower pressure outlet via either an external restriction device or

via an integrally mounted warming valve (as shown below).

Main Steam Line

Drain




Page 1 of 4


Materials and Pipe Class Transitions?

The Function of the DSCV-SA is to pressure reduce and desuperheat the inlet steam to a lower pressure, lower

temperature condition at the outlet. This provides the piping designer with an ideal point at which to transition

the piping class and piping material which are suitable for the downstream (outlet) conditions.

The DSCV-SA is an ideal point at which to make these transitions and due to the construction method employed

within the DSCV-SA philosophy this requirement can easily be accommodated.

The DSCV-SA comprises of a high pressure inlet

section, which is usually constructed from a casting.

The low(er) pressure outlet section is constructed

from a fabrication (cone) and a forging (Outlet

connection & Diffuser plate (where fitted) that

incorporates the steam atomising desuperheater

and water branch connections.

These two components are welded together using

an ASME VIII compliant full penetration butt weld.

The high pressure inlet section is isolated from the lower pressure downstream section at the valve web and

trim’s seating point. At the connection between the two components provides an ideal point at which to make a

pressure rating transition and, where possible, a material transition.




Page 2 of 4

Inlet Connections The inlet connection to the DSCV-SA is usually matched to the inlet pipework in terms of:

• Inlet Piping Size

• Inlet Piping Schedule

• Inlet Piping Material

The DSCV-SA is provided with a range of standard available inlet connection sizes based upon the DSCV-

SA model size employed. The Table below indicates standard available sizes

DSCV-SA Body

Size 0 1 2 3 4 5 6

Available Inlet

Connection Sizes

(Standard)

4”

(DN100)

6”

(DN150)

8”

(DN200)

10”

(DN250)

12”

(DN300)

16”

(DN400)

On

Ap

plica

tion

6”

(DN150)

8”

(DN200)

10”

(DN250)

12”

(DN300)

14”

(DN350)

18”

(DN450)

8”

(DN200)

10”

(DN250)

12”

(DN300)

14”

(DN350)

16”

(DN400)

20”

(DN500)

16”

(DN400)

18”

(DN450)

22”

(DN550)

20”

(DN500)

24”

(DN600)

Where an available standard connection size does not match the customer’s inlet pipework size a standard

concentric reducer can be incorporated onto the inlet connection as shown below

Non Standard Inlet Sizes are accomplished with the use

of a concentric reducer welded to the inlet

This can also be used as a transition piece IF body / pipe

material do not match.




Page 3 of 4

Outlet Connections Due to method of construction, the DSCV-SA can be provided with a virtually infinite range of outlet connection

sizes, ratings and materials to suit any particular application. Downstream pipe size and schedules are usually

matched to the customer pipework requirements, and where possible the outlet material will be matched to the

customer pipework.

In determining the suitability of outlet connection materials and ratings we need to consider a number of

parameters, not only what the customer’s pipework requirements are.

Firstly, we must determine the outlet steam temperature due to an isentropic temperature reduction as the

steam is pressure reduced from inlet conditions to outlet conditions. In this scenario the enthalpy values from

inlet to outlet remain the same and as such no addition of cooling water is taken into account to ensure that

should the cooling water supply fail for any reason, the selected outlet valve materials will be suitable for the

anticipated temperatures. This calculation is performed on the customer provided design parameters (pressure

and temperature) to ensure worst case scenario.

The following is a worked example:

Inlet Design Pressure : 110 bar.a (1595 PSIA) (Information provided by the Customer)

Inlet Design Temperature : 540 deg C (10040F) (Information provided by the Customer)

Outlet Pressure : 25 bar.a (363 PSIA) (control set point) (Information provided by the Customer)

Outlet Design Pressure : 30 bar.a (435 PSIA) (Information provided by the Customer)

Outlet Temperature : 330 deg C (6260F) (Information provided by the Customer)

Based upon the inlet design parameters the valve inlet rating (ASME B16.34) will be:

ASTM A216-WCB - Inlet Design Temperature Exceeds the maximum limit for this material

ASTM A217-WC6 - Inlet Design Temperature Exceeds the maximum limit for this material

ASTM A217-WC9 - ANSI 2500 Standard Class

ASTM A217-C12A - ANSI 1500 Standard Class

Hence depending on the customer’s inlet piping material either an ASTM A217-WC9 or an ASTM A217-C12A

material is suitable for the inlet design parameters.

Based upon the customers provided OUTLET design parameters, we can determine the anticipated outlet rating

(ASME B16.34) and material suitability. The outlet connection of the DSCV-SA is a forged material, hence the

appropriate materials have been specified:

ASTM A105 - ANSI 300 Standard Class

ASTM A182-F11 - ANSI 300 Standard Class



As can be seen, all available outlet materials ‘seem’ to be suitable based upon the customer provided outlet

design conditions.




Page 4 of 4

However, let’s determine what the steam temperature at the outlet of the DSCV-SA will actually be should the

coolant supply fail. We can easily calculate this temperature based upon and Isentropic temperature reduction

where steam enthalpy remains constant.

Inlet Design Pressure : 110 bar.a (1595 PSIA)

Inlet Design Temperature : 540 deg C (10040F) Inlet Design Enthalpy: 3466.4 kJ/kg

Outlet Design Pressure : 30 bar.a (435 PSIA)

Resultant Outlet Temperature : TBA deg C Outlet Design Enthalpy: 3466.4 kJ/kg

Assuming that the steam enthalpy value remains constant from valve inlet to valve outlet, this would result in a

steam temperature of 504.09 deg C (9390F) being experienced at the outlet connection of the valve should the

cooling water supply fail. In this instance, we can recalculate the required ASME B16.34 pressure class and

ascertain the material suitability

Outlet Design Pressure : 30 bar.a (435 PSIA)

Resultant Outlet Temperature : 504.09 deg C (9390F)

ASTM A105 - Inlet Design Temperature exceeds the maximum limit for this material




As can be seen, this re-calculation exceeds the rating previously determined based upon the customer’s provided

outlet design parameters. Due to the expected temperature at the outlet, ASTM A105 is now not a valid option.

Where, based upon the above calculation routine which is incorporated into our sizing calculations, it is not

advisable to comply with a customer specified outlet rating and or material, we shall advise accordingly.

Where further piping material transitions are anticipated after the valve installation (for example a ASTM A335-

P11 to ASTM A106 GrB transition based upon the final achieved outlet steam temperature) we would recommend

that the alloy piping material be maintained for a minimum distance after the valve outlet to allow the

desuperheating process to fully occur. Generally this would be in the range of 5 – 10 meters (16 – 33 feet) after

the valve outlet and is dependent upon a number of factors. Further guidance on individual cases can be sought

from the Copes-Vulcan team.




Page 1 of 3


Where to position the cooling water valve?

The temperature (water) control valve should be located relatively close to the DSCV-SA bypass valve to prevent system lag. The

temperature control valve should also be positioned taking into consideration access for maintenance. Below are some general

guidelines for the positioning and integration of the temperature control valve:

1. It is common practice to have the temperature control valve to be within 10 meters (33 feet) of the water connection of the

DSCV-SA steam bypass valve. This prevents large volumes of water between the temperature control valve outlet and the

DSCV-SA steam turbine bypass valve.

2. If possible the temperature control valve should be positioned at a lower elevation that the DSCV-SA bypass valve to prevent

draining of water into the DSCV-SA bypass valve.

3. The cooling water pipe run after the temperature control valve should be routed so that there are no syphoning loops

created.




Page 2 of 3

4. It is recommended to fit a non return valve between the temperature control valve outlet and the water connection of the

DSCV-SA turbine bypass valve. This ensures that if there is a problem with the cooling water supply when the bypass valve

opens no high temperature steam travels down the water line.

5. The non-return valve inlet connection is an ideal point to transition the water piping material grade. Normally the cooling

water pipe up to the non-return valve inlet is carbon steel. The non-return valve and the water pipe between the NRV outlet

to the bypass water connection is of the same rating and material as the bypass valve outlet.

6. The DSCV-SA can be supplied with water connection in any orientation relative to the steam inlet connection. In the absence

of any information or direction from the customer the water connection will be orientated at 180 degrees from the steam

inlet as the standard default position.

Water connection shown in its

default position.




Page 3 of 3

As can be seen the water connection can be orientated in any position on request. If two or more DSCV-SAs are ordered then the

water connection can be ‘handed’ to further assist the piping engineers and minimise installation pipe work.




Page 1 of 6


Are Hydro and Steam Blowing Trims Available?

YES! On major new build constructions or when major modifications are undertaken at an existing site, the

process of cutting, preparing and welding of new pipes or equipment produces the possibility of entrapping

debris into a piping system.

If this debris is not properly addressed and removed from the system it can cause significant damage to Turbine

Bypass valve trim components, causing not only improper operation of the valve and subsequently the plant, but

also increased maintenance, repair and even replacement of severely damaged trim components.

The best time to resolve this issue is during the construction and commissioning phase.

To avoid any problems with debris the best and most common solution is to flush the line with steam during the

construction / commissioning stage.

The route for this steam flushing (or blowing as it is generally referred) is generally dependant on the piping

installation and can be either:

• Blow Through, or

• Blow Out

Any Steam blowing through (or out) of Turbine Bypass valves requires the use of special equipment. Blow

through valve trims allow the flow of flushing steam and debris to pass through the valve body without damaging

important gasket surfaces and is removed further downstream, blow out valve trims provide a temporary pipe

connection, to which a dedicated flushing line is attached. This vents the flushing steam through the valve bonnet

and is usually directed towards a target plate, this being used to verify the cleanliness of the system.

Steam blowing is usually performed at lower pressures than those experienced during normal system operation.

The flow rate of flushing steam used during this operation should result in a slightly higher dynamic pressure than

that experienced during normal system operation. This ensures that any debris contained within the system can

be transported by the steam and removed.

To assist this operation, specialised steam blowing trims can be provided by Copes-Vulcan.




Page 2 of 6

Steam Blowing Trims – Blow OUT

To protect the operational valve trim from this process it is recommend that the trim be removed and replaced by

a specialised trim designed for the application. The type of equipment needed will be dependent on the system

configuration and how the steam blowing is to be performed.

Depending on the bonnet style employed (Bolted or Pressure Seal) determines the components required for

steam blow out operations

Steam Blow OUT – Bolted Bonnet

Steam Blow OUT (Bolted Bonnet) - Components

(Soft Spares – Gaskets & Gland Packing are also required)

Steam Blow OUT Trim Insert Steam Blow OUT Bonnet




Page 3 of 6

Steam Blow OUT – Pressure Sealed Bonnet

Steam Blow OUT (Pressure Sealed Bonnet) - Components

(Soft Spares – Pressure Seal Ring, Trim Gasket and Gland Packing are also required)

Steam Blow OUT Trim Insert Steam Blow OUT Bonnet




Page 4 of 6

Steam Blow THROUGH – Bolted or Pressure Sealed Bonnet

An additional option is to blow “through” the DSCV-SA into the downstream pipework. In some installations

this may be beneficial to the system, however at some point in the downstream pipework provision should be

made to ensure suitable removal of any entrained debris collected during steam blowing operations. Steam

blowing flow can only be performed over the web. The trim is designed to isolate all critical internal

components during steam blowing operations to ensure debris does not become trapped within the valve

body or trim assembly.

The Large ports incorporated into the design allows for any entrained debris to pass through the valve and

onto the final blow out point.

Steam Blow THROUGH - Components

(Soft Spares – Pressure Seal Ring OR Bonnet Gasket, Trim Gasket and Gland Packing are also required)

Steam Blow THROUGH Trim Insert Gland ‘Bung’




Page 5 of 6

HYDROTEST TRIMS

It is a common misconception that whilst performing a piping system hydrostatic test that the Turbine Bypass

valve can be used as an end of line shut off. It should be noted that using a Turbine Bypass valve in this way is

not recommended practice as these are generally split rated units with the outlet side of the valve being a

much lower rating than the inlet. By applying system hydrostatic test pressure onto a valve trim in the wrong

direction can also cause permanent mechanical damage to the valve stem, balancing arrangement and in

extreme cases the valve actuator. For this reason, Copes-Vulcan can assist by providing a dedicated bi-

directional hydrostatic test trim.

The hydrostatic test trim utilises the trim insert component from the steam blow “out” trim to reduce the

overall quantity and cost of the parts. With the steam blow “out” trim inserted, the operational valve bonnet

is used with the gland packing arrangement removed and a special gland bung being inserted into the gland

area and held in place with the gland bridge. If a steam blow out trim has been purchased, the only additional

component that is required to allow hydrostatic testing to be performed is the dedicated gland bung.

Hydrotest Trim – Bolted Bonnet

Hydrotest Trim (Bolted Bonnet) - Components

(Soft Spares – Gaskets & Gland Packing are also required)

Steam Blow OUT Trim Insert Gland Bung

(Already Available IF Blow Out Trim Components have been Purchased)




Page 6 of 6

Hydrotest Trim – Pressure Sealed Bonnet

Hydrotest Trim (Pressure Sealed Bonnet) - Components

(Soft Spares – Pressure Seal Ring, Trim Gasket and Gland Packing are also required)

Steam Blow OUT Trim Insert Gland Bung

(Already Available IF Blow Out Trim Components have been Purchased)




Page 1 of 15


Are Control Algorithms Available?

YES, and can be supplied as part of the contract documentation.

The aim of this document is to outline the various control options and algorithms that are available.

Steam Turbine Bypass to Condenser

For bypass systems that dump directly to condenser via a dump tube it is often the case that the final steam

temperature or required enthalpy dictates that the steam is at or very close to saturation temperature. This

prevents the use of standard closed loop temperature control due to instrumentation accuracy, full evaporation

of the water cannot be achieved due to relatively short pipe runs and rapid steam velocities or the final enthalpy

target results in steam with a dryness fraction <1.0. In these cases then a feed-forward enthalpy control

algorithm is recommended. The feed-forward enthalpy control algorithm is similar for all applications but can

me modified depending on the available field inputs and measured variables. This FAQ shows typical algorithms.

The feed forward algorithm calculates the amount of cooling water required and the DCS positions the water

control valve accordingly by process measured variables, calculated constants and/or variables.

In its simplest format the water flow rate is based on a standard heat balance calculation. The mass flow rate of

cooling water required for any operating condition of the steam turbine bypass valve can be determined by;

�� =�� ℎ� −ℎℎ −ℎ��

Wc = Water Mass Flow Rate (kg/hr) [calculated]

W1 = Inlet Steam Mass Flow Rate (kg/hr) [measured variable]

h1 = Inlet Steam Enthalpy (kj/kg) [measured variable]

h2 = Outlet Steam Enthalpy (kj/kg) [measured variable]

hw = Cooling Water Enthalpy (kj/kg) [measured variable or can be a fixed constant*]

* If the cooling water pressure and temperature is relatively stable then the enthalpy value can be fixed




Page 2 of 15

1. h1: The measurement of the inlet steam pressure P1 & temperature T1 allows the DCS to determine the

inlet steam enthalpy h1 from steam tables.

2. h2: Is either a fixed target value or can be a sliding value based on the measured downstream pressure

P2 with the DCS determining the enthalpy value from steam tables.

3. hw: Can be a fixed value if the cooling water supply is relatively stable as pressure and temperature

movements in cooling water only have a small effect on the water enthalpy. If the water pressure Pw

and temperature Tw is a measured variable then the DCS can determine the water enthalpy from steam

tables.

4. Qs: The upstream (inlet) steam flow can be a measured variable from a steam flow meter and then

given as an input into the DCS. Alternatively the steam turbine bypass valve lift versus Cv curve can be

used to determine steam flow. Utilising the steam inlet measured values of pressure P1 & temperature

T1 along with the downstream pressure P2 and steam turbine bypass valve lift the steam flow can be

determined from transposing the Cv calculation and a look up routine for the Cv versus lift curve.

5. Qw: The required water flow rate can now be calculated by the simple heat balance calculation shown

above. This calculated water flow rate is then compared to the water flow rate measured variable from

the water flow meter and then the DCS positions the water control valve by constantly matching the

calculated water flow rate to the measured variable water flow rate. Alternatively if a water flow meter

is not available then the water control valve Cv versus lift curve can be used. By measuring the water

pressure Pw and temperature Pt upstream of the water control valve and using the steam downstream

pressure P2 (with the DSCV-SA design steam P2 pressure always equals the water valve P2) the required

water valve Cv can be calculated. Using the water control valve Cv versus lift curve the DCS can position

the water valve accordingly.

It is often the case that a dedicated steam flow meter is not available to measure the inlet steam flow rate

to the steam turbine bypass valve. If a dump tube (sparger) is employed as the final pressure drop device into

the ACC duct or condenser neck then the dump tube can be used as a very effective method to measure the

steam flow.




Page 3 of 15

Calculating Steam Flow Rate to Determine Coolant Flow Rate

Using the Condenser Dump Tube (Sparger) to determine mass steam flow rate

In order to calculate the required water flow rate we utilise the fact that the total flow rate through the dump

tube is a direct function of the pressure inside the dump tube (or within the section between DSCV-SA Valve

outlet and Dump tube inlet). The Total flow through the dump tube is the combination of both superheated

steam flow passing through the DSCV-SA Valve and the water flow used to cool this superheated steam.

We consider that the dump tube is a fixed restriction device allowing for isentropic flow through all of the

individual flow paths of the dump tube. This hypotheses allows us to use a number of relations derived from the

thermodynamic theory of isentropic flow to calculate the total steam flow rate as described below

Determine total steam flow rate passing through the dump tube

Calculated as a function of the dump tube pressure, we utilise the following formula

� = 63.3�� 1�1

Where:

W2 = Total Steam Flow Rate (lb/hr)

Fp = Piping Geometry Factor (assumed as 1.0 if not calculated)

Y = Expansion Factor

� = 1 − �3��

Cv = Installed Dump Tube Cv

X = Pressure Drop Ratio Factor

� = �1 − �2�1

When the value of X = LimX, LimX shall be used.

Where

P2 = Condenser Pressure (psi.a)

LimX = 0.753

P1 = Dump Tube Inlet Pressure (psi.a - Measured Variable)

V1 = Dump Tube Inlet Volume (Determined from steam table by P1 and Target Condenser Enthalpy)




Page 4 of 15

Determine Water Flow Rate

Having previously calculated the total steam flow rate (W2) at the dump tube we use the following equation to

determine the desired cooling water flow

�� =�� −�� −��

H1 = Measurement of the steam turbine bypass valve inlet temperature and inlet temperature will give the inlet

enthalpy (H1) via steam tables.

H2 = The Condenser enthalpy (H2) is the desired condition of the steam in the condenser

Hc = Measurement of the cooling water inlet pressure and inlet temperature will give the cooling water enthalpy

(Hc). Alternatively, as the cooling water temperature is usually low, a fixed design point value can be used

with minimal error.

To provide a degree of adjustability within the system the calculated coolant flow rate can be multiplied by an

adjustable factor to either increase or decrease the calculated coolant flow rate depending upon site

experience.

This calculated water flow rate is then compared to the water flow rate measured variable from the water flow

meter and then the DCS positions the water control valve by constantly matching the calculated water flow rate

to the measured variable water flow rate. Alternatively if a water flow meter is not available then the water

control valve Cv versus lift curve can be used. By measuring the water pressure Pw and temperature Pt upstream

of the water control valve and using the steam downstream (or dump tube) pressure P2 (with the DSCV-SA

design steam P2 pressure always equals the water valve P2) the required water valve Cv can be calculated. Using

the water control valve Cv versus lift curve the DCS can position the water valve accordingly.

Determine Inlet Steam Flow

The Inlet steam flow to the steam turbine bypass valve is calculated as follows

�� =� −��

SPX reserves the right to incorporate our latest design and material changes without notice or obligation. Design features, materials of construction and dimensional data, as described in this bulletin,

are provided for your information only and should not be relied upon unless confirmed in writing.

Page 5 of 15

Turbine Bypass Valve Closed



Page 6 of 15

Turbine Bypass 50% Open



Page 7 of 15





Page 8 of 15

Calculating Steam Flow Rate to Determine Coolant Flow Rate

Using the DSCV-SA Turbine Bypass Valve Characteristic to determine mass steam flow rate

When there is no possibility of using a dump tube to calculate the total mass flow rate, the DSCV-SA Turbine

bypass valve characteristic can be used. The DSCV-SA characteristic is recalculated depending upon the actual

inlet pressure and inlet temperature, which provides the steam flow for different DSCV-SA valve strokes. From

this the cooling water flow rate can be calculated.

a. Determine DSCV-SA Turbine Bypass Valve Characteristics

The inlet pressure and inlet temperature gives two constants, used for correction of the DSCV-SA valve

characteristics to actual operating conditions. These constants are provided in a tabulated format, which are

UNIQUE to each valve and each valve application and are based around a reference condition. The Steam flow is

then calculated based upon the DSCV-SA valves stroke (%) and adjusted for variations in inlet pressure and

temperature from the reference condition as follows: -

�� =�� !��!

Where:

W1 = Calculated Inlet Steam Flow Rate

Wref = Reference Steam Flow Rate based on Valve Lift (%)

K1 = Pressure Constant

K2 = Temperature Constant

An Example of the reference tables are shown below

These Correction Factors are UNIQUE to each valve and each valve application.

Table 1 - Qref - Characteristic Table 2 - K1 - Pressure Constant Table 3 - K2 - Temperature Constant

0% 0.000005% 0.5555610% 0.5555615% 0.5555620% 0.5555625% 0.5555630% 0.5576635% 1.0922540% 2.6368445% 4.4354350% 6.1999555% 7.8953560% 9.3868665% 10.9580070% 12.5734775% 14.1437980% 15.66895

Stroke % Flow (kg/sec)

100% 20.9902495% 19.6791490% 18.48239

325 1.24104300 1.31331

1.11475375 1.14877350 1.18952

105

0.215200.154120.09398

0.39866

0.77182

0.5841640 0.5221035 0.46027

Temperature (Deg C)

K2

525 0.99547519 1.00000500 1.01493475 1.03613450 1.05943425 1.08538400

0.00000

Pressure (bar.a)

75

60

45

30

15

0

5550

7065

2520

85% 17.14893

K1

80 1.0255678 1.00000

0.709030.64647

0.961730.898180.83487

0.337280.27613




Page 9 of 15

Example Calculation:

Calculate the inlet steam flow (W1) based on the following parameters

Valve Lift : 65%

Inlet Pressure : 55 bar.a (Measured Variable)

Inlet Temperature : 475 deg C (Measured Variable)

Wref (table 1) : 10.9580 kg/sec

K1 (table 2) : 0.70903

K2 (table 3) : 1.03613

Therefore

�� = 10.9580�0.70903�1.03613

W1 = 8.05026 kg/sec

b. Determine Cooling Water Flow Rate (Wc)

Having previously calculated the DSCV-SA valve inlet steam flow rate (W1) we use the following equation to

determine the desired cooling water flow

�� =�� −�� −��

H1 = Measurement of the steam turbine bypass valve inlet temperature and inlet temperature will give the inlet

enthalpy (H1) via steam tables.

H2 = The Condenser enthalpy (H2) is the desired condition of the steam in the condenser

Hc = Measurement of the cooling water inlet pressure and inlet temperature will give the cooling water enthalpy

(Hc). Alternatively, as the cooling water temperature is usually low, a fixed design point value can be used

with minimal error.

To provide a degree of adjustability within the system the calculated coolant flow rate can be multiplied by an

adjustable factor to either increase or decrease the calculated coolant flow rate depending upon site

experience.

This calculated water flow rate is then compared to the water flow rate measured variable from the water flow

meter and then the DCS positions the water control valve by constantly matching the calculated water flow rate

to the measured variable water flow rate. Alternatively if a water flow meter is not available then the water

control valve Cv versus lift curve can be used. By measuring the water pressure Pw and temperature Pt upstream

of the water control valve and using the steam downstream (or dump tube) pressure P2 (with the DSCV-SA

design steam P2 pressure always equals the water valve P2) the required water valve Cv can be calculated. Using

the water control valve Cv versus lift curve the DCS can position the water valve accordingly.

This system can also be utilised when a dump tube is not installed – e.g. HP Bypass to Cold Reheat applications.



Page 10 of 15





Page 11 of 15

Required Instrumentation

The MINIMUM required instrumentation for correct operations of the two systems described above as are

follows:

a. When Using the Condenser Dump Tube (Sparger) to determine mass steam flow rate

• Upstream Pressure Transmitter (Valve Inlet)

• Upstream Temperature Transmitter (Valve Inlet)

• Downstream Pressure Transmitter (Dump Tube Inlet)

• Water Flow Meter with High Rangeability (Coolant Valve Inlet)

b. When Using the DSCV-SA Turbine Bypass Valve Characteristic to determine mass steam flow rate

• Upstream Pressure Transmitter (Valve Inlet)

• Upstream Temperature Transmitter (Valve Inlet)

• Water Flow Meter with High Rangeability

Additional Instrumentation

The Following instrumentation applies to both systems and could be considered desirable to improve system

operating efficiencies

• Steam Flow Measurement (Valve Inlet)

• Cooling Water Pressure Measurement (Coolant Valve Inlet)

• Cooling Water Temperature Measurement (Coolant Valve Inlet)

Recommended System Interlocks

The following system interlocks should be considered for incorporation into the control philosophy in order to

protect the turbine bypass valve and interconnecting piping systems.

• Cooling Water Control Valve should be interlocked to the DSCV-SA steam turbine bypass valve to ensure

that the cooling water control valve CANNOT open without the DSCV-SA valve being open and steam

flowing.

• The DSCV-SA should be prevented from opening before the upstream steam temperature has 20 –25 deg C

of superheat. This is to prevent water from passing into the valve.

• To avoid excess water leakage when the bypass system is closed (operating in stand-by mode) it is

recommended that the coolant isolation valve be closed whenever the steam valve is closed.

Other Recommendations for consideration

• In the operating case of Bypass to Condenser, the condenser will need its own trip signals (designed by the

condenser supplier) which will close the bypass system to protect the condenser

• The cooling water supply will usually incorporate a low pressure alarm which should close the bypass system

when coolant pressure falls below a predetermined minimum value to prevent excessively hot steam from

being admitted into the condenser.

• For trip or other events with a known steam flow rate, the control algorithm should be programmed to open

the DSCV-SA bypass valve to a predetermined position before releasing to automatic control mode.




Page 12 of 15

Operational Considerations

The DSCV-SA steam turbine bypass system is design to operate under the following basic modes of operation

• Steam Turbine Trip

• Steam Turbine Start-up

• Steam Turbine Back Pressure Control

Steam Turbine Trip

In case of a Steam Turbine Trip condition, the DSCV-SA Turbine Bypass valve should be opened to a

predetermined position based upon:

• Steam Flow Meter output

• Calibrated Steam Turbine Power Output to Inlet Steam Flow

Once inlet steam flow (i.e. the steam flow rate through the steam turbine just prior to a trip condition) is

established, the DSCV-SA Turbine Bypass characteristic curve can be utilised to determine an appropriate valve

trip ‘open’ position.

Steam Turbine Start-Up

When the Steam turbine is started up after a trip or on initial plant start-up, the DSCV-SA Turbine Bypass Valve

should be gradually closed whilst the turbine is loaded. This operation lasts until the DSCV-SA Turbine Bypass

Valve is closed.

Steam Turbine Back Pressure Control

When the DSCV-SA Turbine Bypass valve is utilised to regulate steam pressure into the Steam Turbine (whether

on fixed or sliding pressure mode) the upstream pressure sensor is utilised to determine DSCV-SA Turbine

Bypass valve position. Steam flow through the DSCV-SA is unlikely to be known (unless independently metered)

and as such the DSCV-SA characteristic curve can be utilised to determine partial bypass flow and associated

cooling water flow rate IF measurement of the downstream temperature is not feasible (i.e. Bypass to

condenser applications)




Page 13 of 15

Fast Opening Turbine Bypass Valve & Coolant Valve Operating Philosophy

In case of a Steam Turbine Trip condition, the DSCV-SA Turbine Bypass valve should be opened to a

predetermined position based upon:

• Steam Flow Meter output

• Calibrated Steam Turbine Power Output to Inlet Steam Flow

Once inlet steam flow (i.e. the steam flow rate through the steam turbine just prior to a trip condition) is

established, the DSCV-SA Turbine Bypass characteristic curve can be utilised to determine an appropriate valve

trip ‘open’ position. Below is a basic philosophy of how this can be incorporated into the valve control system.

The data is constantly measured by the DCS and the calculations below are continuously performed so that at

any load when a trip occurs the steam turbine bypass system is in a state on continual readiness

1 2

3

4

5 6 7

8 9 10 11 12




Page 14 of 15

Steam flow to be bypassed (i.e. the steam flow rate through the steam turbine just prior to a trip

condition) is established together with the Inlet Pressure and inlet temperature measurements

Cv Calculation. The Cv (Valve Capacity) is determined by the above inlet operating conditions and the

required outlet pressure. This determines the DSCV-SA percentage (%) opening and 4-20mA command

signal. Under emergency Trip conditions the condenser will be at normal operating pressure (Either a

measured variable or fixed for the purpose of trip condition) and therefore a Cv calculation can be

performed.

After calculating the required condition Cv for the DSCV-SA the corresponding opening percentage is

determined from the DSCV-SA Cv vs Percentage lift curve. This is converted to the 4-20mA command

signal

To ensure a ‘clean’ stable reading the signal is passed through a 2 second delay timer and sample and

hold loop. This prevents erroneous readings at the time of a trip condition. Due to the normal scan

times of most DCS systems which can be 200 to 300 milliseconds and the rapid response of the steam

turbine isolation valve. Without a sample delay loop steam flows may have significantly reduced when

the next can captures the steam flow rate

The Enable Switch is activated by the Turbine Trip Alarm

The Adjustable ramp down timer is initiated on Turbine Trip. This decays the calculated command signal

over the adjustable time period, normally set for approximately 10 seconds. However this time is

adjustable and can be tuned to specific site installations.

The High Selector receives the calculated command signal from point (3) above, which is now being

constantly reduced over a period of time set in the ramp down timer. It also receives the PIC loop

command signal which is now catching up after the turbine trip. The Hi-Selector only allows the highest

of these two command signals through to the DSCV-SA Turbine Bypass Valve positioner. As soon as the

PIC loop command signal is greater than the continuously reducing calculated command signal the

DSCV-SA Turbine Bypass bumplessly transfers to PIC control.

In some instances, where pneumatic actuator are utilised, it may prove beneficial to utilise a fast start

solenoid valve (not shown in system diagram). A Fast start adjustable timer is required to give an initial

digital signal to a 3/2 override solenoid valve fitted to the actuators pneumatic control circuit. This

digital signal is held for approximately 1.5 seconds and is adjustable to allow for tuning during system

commissioning. The Solenoid valve diverts instrument air directly into the valve actuator which opens

the valve bypassing the valve positioner. This short burst of instrument air into the actuator will open

the DSCV-SA Turbine Bypass valve by approximately 25-40% which negates the initial delay if only the

calculated command signal was applied to the valve positioner.

For the first few seconds of operation of the desuperheating algorithm (used to determine coolant flow

rate) cannot be used as the pressure in the dump tube is unstable. However the relationship of

percentage lift of the DSCV-SA Turbine Bypass Valve and the percentage lift of the water control valve

can be used. Having already determined the required DSCV-SA Turbine Bypass Valve lift then the

corresponding water control valve lift (command signal) can be determined from the DSCV-SA

percentage lift versus water control valve percentage lift curve.

1

2

3

4

5

6

7

8




Page 15 of 15

Enable switch activated by Turbine Trim Alarm

The Adjustable ramp down timer (if required, not shown) is initiated on Turbine Trip. This decays the

calculated command signal over the adjustable time period, normally set for approximately 10 seconds.

However this time is adjustable and can be tuned to specific site installations.

The adjustable bias is for fine tuning during commissioning to allow for any inaccuracies in the

calculated results and the overall plant set-up

The High Selector receives the calculated command signal from point (8) above, which is now being

constantly reduced over a period of time set in the ramp down timer. It also receives the PIC loop

command signal which is now catching up after the turbine trip and pressure starts to stabilise in the

dump tube. The Hi-Selector only allows the highest of these two command signals through to the water

control valve positioner. As soon as the desuperheating algorithm command signal is greater than the

continuously reducing calculated command signal the water control valve bumplessly transfers to

algorithmic control

In some instances, where pneumatic actuator are utilised, it may prove beneficial to utilise a fast start

solenoid valve (not shown in system diagram). A Fast start adjustable timer is required to give an initial

digital signal to a 3/2 override solenoid valve fitted to the actuators pneumatic control circuit. This

digital signal is held for approximately 1.5 seconds and is adjustable to allow for tuning during system

commissioning. The Solenoid valve diverts instrument air directly into the valve actuator which opens

the valve bypassing the valve positioner. This short burst of instrument air into the actuator will open

the water control valve by approximately 20-40% which negates the initial delay if only the calculated

command signal was applied to the valve positioner.

9

10

11

12




Page 1 of 6

DSCV-SA FAQs – 24: MAINTENANCE

Are Any Special Tools Required?

The DSCV-SA is not a high maintenance valve - the Copes-Vulcan engineering team were tasked with ‘easy

maintenance’ within their design brief.

The complete trim is a ‘Quick-Change’ style with no welded in components or large internal threaded parts. The

whole trim assembly is held in compression by either a compression ring or the bonnet. By simply removing the

compression ring or bonnet the whole trim simply slides out of the top of the valve. Therefore in-situ

maintenance, should it be required, is both expeditious and uncomplicated with no need for any specialised

tooling or training.

The DSCV-SA can usually be maintained with standard maintenance tooling that is normally available within most

power plant maintenance departments.

However, SPX does provide service assistance fixtures to assist the client with performing maintenance activities

should they be required. These service assistance fixtures are utilised when large DSCV-SA’s are installed in a

horizontal orientation as the trim components can be of considerable weight and as such can prove difficult for

maintenance personnel to manually handle.




Page 2 of 6

INSTALLATION ORIENTATION:

Actuator Vertically Upwards with outlet vertically downwards

In this orientation provision should be made for a fixed lifting point suitable for the installation of a chain block (or

similar) to ease any future maintenance interventions. The Lift point should ideally have a SWL of 5 tonnes

(11,000 lbs) (Note that this SWL can be reduced where smaller DSCV-SA sizes are installed).

Large Trim components within the DSCV-SA are provided with blind drilled and tapped holes to allow lifting eyes

to be installed. The chain block is then employed to simply ‘lift’ the trim components from the valve.




Page 3 of 6


Actuator Horizontal with outlet Horizontal

In this orientation removal of the trim components can be a little more difficult than in a vertically (Outlet

downwards) installation simply due to the weight involved in the trim components of larger size DSCV-SA valves.

A simple service assistance fixture may assist the site maintenance personnel in removing and installing the larger

trim components within the assembly.

As per the previous orientation provision should be made for a fixed lifting point suitable for the installation of a

chain block (or similar) to ease any future maintenance interventions. The Lift point should ideally have a SWL of 5

tonnes (Note that this SWL can be reduced where smaller DSCV-SA sizes are installed).

The Service Assistance fixtures are:

• Designed to assist service technicians with the removal of heavy trim components

• Multiple designs available depending on space availability and orientation

• Not required for actuator vertically upwards / outlet vertically downwards installations




Page 4 of 6


Actuator Horizontal with outlet Horizontal

Example of Service Assistance Fixture installed in DSCV-SA Valve.

Example of Service Assistance Fixture ready for shipment.




Page 5 of 6


Actuator Vertically Downward with outlet vertically upwards

Whilst the DSCV-SA can be installed in this orientation it is not recommended practise as this results in any future

required maintenance being extremely difficult to perform. In this orientation it is strongly recommended that

service assistance fixtures are utilised to enable removal and subsequent installation of the valve trim

components.




Page 6 of 6


Actuator Vertically Downward with outlet vertically upwards

Service Assistance Fixtures for Outlet Vertically Upward installations




Page 1 of 1


Are Specialist Field Service Engineers or Special Training Required?

NO! The DSCV-SA is not a high maintenance valve - the Copes-Vulcan engineering team were tasked with ‘easy







The DSCV-SA can usually be maintained with standard maintenance tooling that is normally available within most

power plant maintenance departments. Anyone with experience of maintaining normal globe control valves will

have sufficient knowledge and experience to tackle maintenance interventions of the DSCV-SA.

Of course, SPX can provide qualified field service engineers to perform on-site maintenance works should the

client / end user not have sufficient capacity or manpower to perform maintenance during a major planned plant

shutdown.




Page 1 of 3


Does the valve have a ‘Quick-Change’ trim design?

YES! The DSCV-SA is not a high maintenance valve - the Copes-Vulcan engineering team were tasked with ‘easy










Page 2 of 3

DSCV-SA WITH BOLTED BONNET (Applicable to Valves with a Pressure Class Rating of ANSI 900 or less)

DSCV-SA is shown with a BOLTED bonnet arrangement. The Bonnet holds the spacer and cage in compression.

Trim Spacer

Bonnet Gasket

Bonnet

Cage Assembly

Trim Gasket

Anti-Rotation Ring




Page 3 of 3

DSCV-SA WITH PRESSURE SEALED BONNET (Applicable to Valves with a Pressure Class Rating of ANSI 1500 or Higher)

Trim Spacer

Cage Assembly

Trim Gasket

Anti-Rotation Ring

Compression Ring

Bonnet




Page 1 of 5

DSCV-SA FAQs – 27: MANUFACTURE

Typical Inspection and Test Plans (ITP)

There are a number of standard inspection and test plans available depending on the level of certification

required, where the valve will be installed and the required design code. The table below should enable you to

make an appropriate selection.

All inspection and test plans can be modified and adjusted to meet specific customer and/or end user

requirements of the specific project.

ITP Designation

Number

Material

Certification Level

Valve Design Code CE Marked Applicable Welding

Specification

ITP 19 3.1 ASME VIII NO WS/402

ITP 20 3.1 ASME VIII YES WS/402

ITP 65 3.1 EN 13445 NO WS/452

ITP 66 3.1 EN 13445 YES WS/452

Description : 3.1 Certification, DSCV-SA with Seat Leakage TestDesign Code : ASME VIII

Inspector : 1 = Manufacturer = Copes-Vulcan / Sub-Vendor2 = Customer / Representative

Surveillance : H = Hold PointM = Mandatory Hold PointR = Review Point

Installation, Operation & Maintenance Manual (IOM) Format & Quantity For Review None

Manufacturing Record Book (MRB) Format & Quantity For Review None

No. Procedure or Specification Verifying Document& Acceptance Criteria (#) = In Manufacturing Record Book 1 2

1 Inspection & Test Plan Inspection & Test Plan Inspection & Test Plan (#) H R2 Pre-Inspection Meeting None None3 Material Tests for Pressure Retaining Components Material Specification Certificate per EN 10204 3.1 (#) H R3.1 Body, Bonnet, Bonnet Spacer, Branches, Reducers

Flanges as applicable4 Surface Quality Check for Pressure Retaining Castings MSS SP55 Certificate H4.1 Body, Bonnet as applicable5 Material Tests for Pressure Retaining Fasteners Material Specification Certificate per EN 10204 3.1 H5.1 Bonnet Studs & Nuts as applicable6 Material Tests for Major Trim Components Material Specification Certificate per EN 10204 2.1 H6.1 Plug, Seat, Cage, Stem as applicable7 Material Check for Other Components Material Specification Certificate per EN 10204 2.1 H7.1 Minor Trim Parts, Gland Parts, Gaskets, Seals,

Packing, Actuator as applicable8 Welding of Pressure Retaining Components Welding Dossier (#) H R

Weld MapWelding Procedure Specification (WPS)Procedure Qualification Record (PQR)Welder QualificationHeat Treatment Chart for

8.1 Casting Repair as applicable ASME B16.348.2 DSCV-SA Body WS/4029 NDE of Pressure Retaining Components NDE Dossier (#) H R

NDE ProcedureNDE Operator QualificationNDE Report for

9.1 Raw Materials None9.2 Weld Repairs of Castings as detemined by ASME B16.34

manufacturer as applicable9.3 DSCV-SA Body welds WS/40210 Material Hazardous Area Protection None None11 Visual, Dimensional & Surface Quality Check Contract Drawing Certificate H12 Hydrostatic Test ASME B16.34 Certificate (#) M R13 Seat Leakage Test (Water test only) ANSI / FCI 70-2 Certificate (#) H R14 Function Test Factory Acceptance Test Sheet Certificate (#) H R14.1 Stroke, Handwheel, Instrumentation as applicable15 Marking, Tagging & Painting Labelling Sheet & Paint Specification Certificate H16 Packing & Shipment Preparation Plenty Working Procedure 4.13.02 Certificate H17 Certificate of Conformity Customer Purchase Order Certificate (#) H R18 CE Declaration of Conformity None None19 Documentation Review Inspection & Test Plan Manufacturing Record Book H R

00 CMRREV MADE BY

Original Issue 18-Mar-10DESCRIPTION DATECHECKED BY

BRH

Document No. ITP19

Inspection & Test Plan

Activity Surveillance

As Final 1 CD

As Final 1 CD

Sheet 1 of 1

Description : 3.1 Certification, CE Marked, DSCV-SA with Seat Leakage TestDesign Code : ASME VIII










8.1 Casting Repair as applicable ASME B16.348.2 DSCV-SA Body WS/4029 NDE of Pressure Retaining Components NDE Dossier (#) H R


9.1 Raw Materials None9.2 Weld Repairs of Castings as detemined by ASME B16.34

manufacturer as applicable9.3 DSCV-SA Body welds WS/40210 Material Hazardous Area Protection None None11 Visual, Dimensional & Surface Quality Check Contract Drawing Certificate H12 Hydrostatic Test ASME B16.34 Certificate (#) M R13 Seat Leakage Test (Water test only) ANSI / FCI 70-2 Certificate (#) H R14 Function Test Factory Acceptance Test Sheet Certificate (#) H R14.1 Stroke, Handwheel, Instrumentation as applicable15 Marking, Tagging & Painting Labelling Sheet & Paint Specification Certificate H16 Packing & Shipment Preparation Plenty Working Procedure 4.13.02 Certificate H17 Certificate of Conformity Customer Purchase Order Certificate (#) H R18 CE Declaration of Conformity PED 97/23/EC Certificate (#) H R19 Documentation Review Inspection & Test Plan Manufacturing Record Book H R

00 CMRREV MADE BY

Original Issue 18-Mar-10DESCRIPTION DATECHECKED BY

BRH

Document No. ITP20



As Final 1 CD

As Final 1 CD

Sheet 1 of 1

Description : 3.1 Certification, DSCV-SA with Seat Leakage TestDesign Code : EN 13445










8.1 Casting Repair as applicable EN 125168.2 DSCV-SA Body WS/4529 NDE of Pressure Retaining Components NDE Dossier (#) H R


9.1 Raw Materials None9.2 Weld Repairs of Castings as detemined by EN 12516

manufacturer as applicable9.3 DSCV-SA Body welds WS/45210 Material Hazardous Area Protection None None11 Visual, Dimensional & Surface Quality Check Contract Drawing Certificate H12 Hydrostatic Test EN 12516 Certificate (#) M R13 Seat Leakage Test (Water test only) ANSI / FCI 70-2 Certificate (#) H R14 Function Test Factory Acceptance Test Sheet Certificate (#) H R14.1 Stroke, Handwheel, Instrumentation as applicable15 Marking, Tagging & Painting Labelling Sheet & Paint Specification Certificate H16 Packing & Shipment Preparation Plenty Working Procedure 4.13.02 Certificate H17 Certificate of Conformity Customer Purchase Order Certificate (#) H R18 CE Declaration of Conformity None None19 Documentation Review Inspection & Test Plan Manufacturing Record Book H R

00 CMRREV MADE BY

Document No. ITP65



As Final 1 CD

As Final 1 CD

BRH 18-Mar-10DATECHECKED BYDESCRIPTION

Original Issue

Sheet 1 of 1

Description : 3.1 Certification, CE Marked, DSCV-SA with Seat Leakage TestDesign Code : EN 13445










8.1 Casting Repair as applicable EN 125168.2 DSCV-SA Body WS/4529 NDE of Pressure Retaining Components NDE Dossier (#) H R


9.1 Raw Materials None9.2 Weld Repairs of Castings as detemined by EN 12516

manufacturer as applicable9.3 DSCV-SA Body welds WS/45210 Material Hazardous Area Protection None None11 Visual, Dimensional & Surface Quality Check Contract Drawing Certificate H12 Hydrostatic Test EN 12516 Certificate (#) M R13 Seat Leakage Test (Water test only) ANSI / FCI 70-2 Certificate (#) H R14 Function Test Factory Acceptance Test Sheet Certificate (#) H R14.1 Stroke, Handwheel, Instrumentation as applicable15 Marking, Tagging & Painting Labelling Sheet & Paint Specification Certificate H16 Packing & Shipment Preparation Plenty Working Procedure 4.13.02 Certificate H17 Certificate of Conformity Customer Purchase Order Certificate (#) H R18 CE Declaration of Conformity PED 97/23/EC Certificate (#) H R19 Documentation Review Inspection & Test Plan Manufacturing Record Book H R

00 CMRREV MADE BY

Document No. ITP66



As Final 1 CD

As Final 1 CD

BRH 18-Mar-10DATECHECKED BYDESCRIPTION

Original Issue

Sheet 1 of 1

DSCV - FREQUENTLY ASKED

QUESTIONS

DSCV-SA FAQ:140109-01

SPX reserves the right to incorporate our latest design and material changes without notice or obligation.

Design features, materials of construction and dimensional data, as described in this bulletin, are provided for your information only and should not be relied

upon unless confirmed in writing. Please contact your local sales representative for product availability in your region. For more information visit

www.spx.com.

The green “>” is a trademark of SPX Corporation, Inc.

ISSUED 03/2014 CV-DSCV-FAQ

COPYRIGHT © 2014 SPX Corporation

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